RU21239U1 - VORTEX FLOW METER CONVERTER - Google Patents

Description

Vortex Flowmeter Converter

The utility model relates to measuring technique and can be used in flow measurement to measure the flow of gaseous and liquid media in a vortex way ..

A known vortex flowmeter transducer is fixed in the pipeline by means of an installation flange, comprising a sensing element and a flow body including a front vortex-forming plate, an intermediate and an end section. The sensitive element is made in the form of a rigid rod placed in the through groove of the intermediate section of the flow body and connected to a tube fixed inside the mounting flange; two piezoelectric elements are placed inside the tube, made in the form of half cylinders, electrically isolated from each other, and the groove on both sides is closed by two membranes connected to a rigid rod. The through groove of the intermediate section of the flow body is made from the mounting flange. The flow body is placed symmetrically with respect to the inner diameter of the flow part of the pipe (1).

The incident flow of a moving medium is separated by the flow body and vortices are formed, alternately along and behind each wall of the flow body, the frequency of which is directly proportional to the speed of the medium. The formation of vortices is accompanied by the creation of a pressure differential between the sides of the body around the flow and causes a deflection of the membranes

sensing element, which, in turn, creates a movement of the rigid rod into the groove, leading to the bending of the tube into which the rod passes. When bent, the tube is deformed. assuming the shape of an ellipse in the cross section and compressing the piezoelectric element, which converts the mechanical compressive force into an electrical signal that changes with the frequency of vortex formation.

The sensing element is located in the area adjacent to the inner surface of the pipe. The interaction of the medium flow with the pipe surface contributes to the generation of additional vortices in the zone adjacent to its end part on the flow around the body. Pressure pulsations created by additional vortices are perceived by the sensitive element and create interference that degrades the quality of the main signal. If the signal-to-noise ratio (the ratio of the amplitude of the useful signal to the amplitude of the interference signal) is less than three, the electronic unit determines the fundamental vortex frequency with an unacceptably large error and the device loses its ability to measure the flow rate of the medium. This phenomenon is observed at relatively low velocities of the measured medium, since the amplitude of the useful signal is determined by the magnitude of the amplitude of the pulsations of the alternating pressure pxV2 / 2 (here p is the density of the medium, V is the velocity of the measured medium), and decreases in proportion to the square of the velocity.

Another design disadvantage is the low vibration resistance of the sensing element, since the systekg from the rod and membranes has a relatively large moment of inertia, which is determined by

design features of the sensor - the rod must be sufficiently rigid and strong, and therefore must have a cross-sectional area that provides these properties. Vibration creates an inertial moment M mxaxl / 2 (here the t-mass of the rod; a-vibration acceleration; 1-length of the rod), which deforms the tube and compresses the piezoelectric element. The piezoelectric element produces an electrical signal that is a nuisance and pollutes the main signal. At high values of vibration acceleration (more than 0.3 m / s2), the noise signal clogs the main one, i.e. the signal-to-noise ratio becomes less than three, and the device stops calculating the correct flow rates.

The closest in technical essence to the claimed solution is a vortex flowmeter transducer mounted in the pipeline by means of an installation flange. The transducer comprises a flow body having a front vortex-forming plate with a smooth front surface on the flow inlet side and beveled side surfaces, an intermediate section in the form of a rod in which the sensing element is placed, and an end section. The sensing element is made in the form of a capsule filled with oil. The sides of the capsule are flexible membranes flush with the flat surfaces of the intermediate section of the body flow. Through these membranes, alternating pressure pulses are transmitted from the vortices from the side surfaces of the rod through an oil layer to a sensitive element made in the form of a ceramic disk having piezoelectric

properties. The AC voltage signal generated by this element is transmitted through a conductive conductor to an amplifier to obtain a flow signal suitable for transmission over relatively long distances (2).

This design is not vibration resistant, since the oil layer between the membranes and the piezoelectric element has a sufficiently large mass. When exposed to vibration, this layer, together with the piezoelectric element, oscillates under the influence of force (here, t is the mass of the oil layer between the sensing element and the membrane; a is vibration acceleration). The oil layer periodically with a force F acts on the piezoelectric element, which produces a noise signal that is directly proportional to the mass t. The signal-to-noise ratio becomes unacceptably small even with small vibration accelerations that occur during operation of the device. The effect is especially noticeable at low costs, where the signal-to-noise ratio is small - the electronic unit stops processing the signal, which leads to a decrease in the dynamic range of the device. The sensitivity of the device is determined by the area of the piezoelectric element and the magnitude of the pressure acting on the piezoelectric element. In this design, the pressure difference on both sides of the flow body is perceived by one piezoelectric element through two flexible membranes, the rigidity of which limits the magnitude of this pressure. Therefore, the signal-to-noise ratio decreases, starting from a certain flow rate, where vibration acceleration increases, and the amplitude of the useful signal remains constant.

Another disadvantage of the device is the immunity of the sensing element to the additional vortices that the body flows around the inner wall of the pipeline. The location of the sensing element on the body of the flow around is not specified and in real structures it is usually located at a distance from the end of the body of the flow around less than 0.2 diameter of the pipeline due to technological difficulties that arise when drilling long holes between the capsule and the end of the body of the flow around, large diameters of pipelines. In addition, such a design is operable only in a narrow temperature range, since all liquids (including oil) have a large coefficient of thermal expansion. At elevated temperatures, swelling first occurs and then the membrane ruptures. The device fails.

The objectives of the proposed technical solution are: expanding the dynamic range of the device in the direction of measuring low costs by increasing the signal-to-noise ratio at these costs; increasing the resistance of the device to vibration and increasing the reliability of the device.

To achieve the technical result, a device is proposed which, like the prototype, contains a sensing element and a flow body, including a front vortex-forming plate, an intermediate and end section, the sensitive element is made in the form of two membranes located on the flat surfaces of the intermediate section of the flow body symmetrically to its axis and piezoelectric element. Unlike

of the known device, the vortex flowmeter transducer is equipped with an additional piezoelectric element, grooves closed by membranes are made on opposite surfaces of the intermediate section of the flow body, piezoelectric elements fixed at grooves located at a distance from the inner surface of the pipeline exceeding 0.2 of its internal diameter, and the space between the membranes and piezoelectric elements is filled a binder with dielectric properties. In addition, the flow around the body is made of a dielectric, for example, aluminum oxide, and the membranes of the sensing element and the binder are made of high molecular weight polyethylene.

A plate piezoelectric element is used instead of a disk-shaped piezoelectric element as a converter of pressure pulsations to an electrical signal, and a binder dielectric material is used instead of the oil in the capsule between the piezoelectric element and the membrane. The recesses under the piezoelectric elements are made at a distance from the inner surface of the pipeline in excess of 0.2 of its diameter. The body of the flow can be of any, but not a special shape. The flow body can be made of a dielectric, for example, aluminum oxide, whose elastic modulus is greater than that of steel, and the membranes can be not metal, but from a dielectric, for example, of high molecular weight polyethylene, which can also play the role of a binder.

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The dynamic range of the proposed device is increased by increasing the signal-to-noise ratio at low costs. Signal to noise ratio improved by:

-reducing the influence of the noise signal from additional vortices on the useful signal due to the installation of the piezoelectric element at a distance from the inner surface of the pipeline exceeding 0.2 of its inner diameter: -increasing vibration resistance by changing the design of the sensitive element and introducing an additional piezoelectric element. This allows, firstly, to suppress the noise signal from the effects of vibration by obtaining the total signal from the piezoelectric elements operating in antiphase, and secondly, to double the useful signal since the pressure pulses acting on the piezoelectric elements are shifted by half the period and thereby the signal-to-noise ratio improves and thirdly, to reduce the mass that creates the pressure force on the piezoelectric element when exposed to vibration acceleration;

- manufacturing a flow body from a material with a higher elastic modulus than steel - this increases the rigidity of the body structure of the flow around, which reduces the amplitude of its vibrations and, accordingly, reduces the deformation of the piezoelectric element, and hence the noise generated by the electric signal from vibration.

Improving the reliability of the device is achieved due to:

-replacements of the material of the flow body and the membrane material to a dielectric, which excludes the closure of the piezoelectric electrodes through the membrane and the body

flow around. In the manufacture of the sensing element, it is possible to touch the electrodes of the piezoelectric element of the membrane or body flow;

- changes in the design of the sensitive element and the replacement of oil with a binder material, which eliminates the destruction of membranes during water hammer.

The utility model is illustrated by drawings: in Fig. 1, a vortex flowmeter transducer mounted in a pipeline; figure 2 is a section aa in figure 1 is a cross section of the body of the flow around the attachment of the sensing element; on figs - view B in fig. 1; on fsh. 4 and 5 spectrograms of signals, respectively, with the peripheral and central location of the piezoelectric elements relative to the inner diameter of the flowing part of the pipeline.

The vortex flowmeter transducer comprises a flow around body 1 consisting of a front vortex-forming plate 2, an intermediate section 3, and an end section 4. The transducer is installed in the pipeline 5 by means of a mounting flange (not shown in the drawing). The body of the flow around 1 is placed symmetrically with respect to the inner diameter of the flowing part of the pipeline 6. The swirl plate 2 has a smooth front surface 7 on the flow side and beveled side surfaces 8. An intermediate section 3 of rectangular section is attached to the rear surface of the plate 2. On the flat surfaces 9 of the intermediate section symmetrically to the axis of the body of the flow around the grooves are made 10. The sensitive element is made in the form of two identical plate piezoelectric elements 11,

fixed in the grooves 10, and flexible membranes 12, closing the grooves 10 and attached flush around the perimeter of the membranes to the surfaces 9 of the intermediate section 3 of the body flow. The membranes 12, the piezoelectric elements 11 and the flow around the body 1 are fastened together by a bonding material 13. The piezoelectric elements 11 are equipped with wires 14, which are drilled through 15 to the electronic unit (not shown) to amplify and process the signal. The piezoelectric elements 11 are placed in the grooves 10 at a distance h from the internal flowing part of the pipeline 6, exceeding 0.2 of its diameter.

Converter vortex flowmeter operates as follows.

When a flow of a moving medium flows around the body 1, the flow is divided by the sharp edges of the plate 2 and vortices are formed, alternately along and behind each side of the body 1. When the vortices form, a pressure differential is created between the sides of the flow around the body. Pressure pulsations through the membranes 12 and the layer of binder material 13 are perceived by piezoelectric elements 11, which convert the mechanical compression force into an electrical signal that varies with the frequency of vortex formation proportional to the flow rate of the medium.

As an example, Figures 4 and 5 show spectrograms of signals generated by two sensitive elements at low gas flow rates. The sensitive elements were two pairs of identical piezoelectric elements embedded in symmetrical recesses on the sides of the flow body. One pair was located on the peripheral part no further than 0.2

the diameter of the flowing part from its inner wall, and the second is in the central part of the flow body. A comparison of spectrograms shows that the signal from the peripheral sensing element has a lower frequency than from the central one. This is explained by the presence of additional vortices in the zone adjacent to the inner surface of the flowing part. Additional vortices are formed due to the interaction of the measured medium flow not only with the flow body, but also with the inner surface of the flow part. The signal, perceived by the central sensing element, is created mainly by the main vortex, a vortex, formed due to the interaction of the flow only with the body around it. The effect of the additional vortices removed from it affects rather weakly. The signal-to-noise ratio is more favorable - i.e. exceeds 3. Such a signal is easily processed by the electronic unit. At the same time, the signal from the peripheral sensing element has a signal-to-noise ratio of less than 3 and is not processed by the electronic unit. The dynamic range of the device (the ratio of the largest measured flow rate to the smallest) decreases. Otherwise, it is necessary to significantly complicate the electronic circuitry of the unit, which will lead to an increase in the cost of the device when its metrological characteristics deteriorate, even a complicated scheme does not allow determining the frequency of vortex formation by the body around the flow with sufficient accuracy.

USEFUL MODEL FORMULA

I. A vortex flowmeter transducer fixed in the pipeline and containing a sensing element and a flow body, including a front vortex-forming plate, an intermediate and end section, the sensitive element is made in the form of two membranes located on the flat surfaces of the intermediate section of the flow body symmetrically to its axis and piezoelectric element, characterized the fact that the vortex flowmeter transducer is equipped with an additional piezoelectric element, on opposite surfaces of the intermediate section of the flow body grooves closed by membranes are made, piezoelectric elements fixed at grooves located at a distance from the inner surface of the pipeline exceeding 0.2 of its inner diameter are made, and the space between the membranes and the piezoelectric elements is filled with a binder dielectric material.

2. The vortex flowmeter transducer according to claim 1, characterized in that the flow body is made of a dielectric, for example, aluminum oxide.

3. The flowmeter converter according to claim I, characterized in that the membranes of the sensing element and the binder material are made of high molecular weight polyethylene.

Claims (3)

1. The vortex flowmeter transducer mounted in the pipeline and containing the sensing element and the flow body, including the front vortex-forming plate, the intermediate and end sections, the sensitive element is made in the form of two membranes located on the flat surfaces of the intermediate section of the flow body symmetrically to its axis and piezoelectric element, characterized the fact that the vortex flowmeter transducer is equipped with an additional piezoelectric element, on opposite surfaces of the intermediate section of the flow body grooves closed by membranes are made, piezoelectric elements fixed at grooves located at a distance from the inner surface of the pipeline exceeding 0.2 of its inner diameter are made, and the space between the membranes and the piezoelectric elements is filled with a binder dielectric material.  2. The vortex flowmeter transducer according to claim 1, characterized in that the flow body is made of a dielectric, for example, aluminum oxide. 3. The flowmeter Converter according to claim 1, characterized in that the membranes of the sensing element and the binder material are made of high molecular weight polyethylene.