RU2123668C1 - Method of measuring of liquid and gaseous media flow rate - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: flow rate is measured by measuring the frequencies of combination waves (summary and difference frequencies). Use is made of acoustic waves, frequencies of which are close to each other. Waves propagate towards each other, and their fronts fill all points of pipeline transverse section. Excitation of probing signals and reception of information signals are performed from side of pipeline external surface (method remains contactless, and pipeline integrity is not disturbed). Given method features superhigh sensitivity due to extra fast propagation of waves of summary frequency which allows measurement of flow rate of less than 10^-3 m/s. Method is characterized by simplicity of measurement principle and electronic circuit. EFFECT: removed auxiliary (circuit) errors, enhanced reliability. 1 dwg

Description

 Use - in flow measurement. The inventive method for measuring liquid and gaseous media lies in the fact that the flow is probed by superimposing two counterpropagating plane acoustic waves with similar frequencies of the interference wave of the total and difference frequencies, the frequency values of which determine the flow rate.

 The invention relates to flow measurement and improves the accuracy of measuring the flow rate of liquid and gaseous media using acoustic waves.

 A known method of measuring the flow rate [1] by the frequency offset of the Doppler type, according to which the flow rate is determined by the magnitude of the change in the frequency of traveling plane longitudinal acoustic waves that occur during the "collapse" - the transfer of part of the energy of cylindrical waves from the axial region near the boundary with the medium without cylindrical waves, through its “end” surface, into the region without cylindrical waves.

 However, in this method, it is necessary to use short pulses and a reference circuit for a certain number of received waves, followed by the start of a new pulse, which limits the sensitivity of the method and the accuracy of the flow measurement.

 The technical result, the solution of which the invention is directed, is to increase the accuracy of measuring the flow rate of liquid and gaseous media.

This is achieved by the fact that the flow in the measuring section of the pipeline, which, unlike [1], can have an arbitrary shape: cylindrical, elliptical, rectangular, etc., is probed by waves propagating towards each other with close frequencies ω ₁ , ω ₂ , fronts which fill all the points of the radial section of the pipeline, and the flow rate is determined by the magnitude of the frequencies ω ₁ , ω ₂ formed in the overlapping region of the primary waves, the frequencies of the combination waves — total and difference.

частот, имеющих резко отличающиеся скорости распространения: суммарной частоты

и разностной

Из приведенной зависимости для скорости волны суммарной частоты следует возможность неограниченно больших (с позиций "сплошной" среды) значений V_c; в этих выражениях c - скорость звука в среде. При движении среды в трубопроводе со скоростью U, частоты

изменяются на величину, пропорциональную средней, по площади поперечного сечения трубопровода, скорости:

или - расходу

, где S - площадь поперечного (радиального) сечения трубопровода.The essence of the method is as follows. On the measuring section of the pipeline in the medium that fills it, running opposite to each other are created - oncoming plane waves with frequencies close to each other ω ₁ , ω ₂ . In the case of a cylindrical pipeline, such waves are generated by “collapsing” on the longitudinal cylindrical axis of the cylindrical waves emitted by the cylindrical emitters of acoustic waves mounted on the outer surface of the pipeline. If the pipeline has a non-cylindrical shape, then similar plane waves are formed during the introduction, also from the outside of the surface, of plane waves at an acute angle to the longitudinal axis of the pipeline section, at a certain distance from the injection site. Due to the fact that the most common are cylindrical pipelines, only cylindrical pipelines are considered below (the difference is only in the way of creating plane acoustic waves running towards one another). In the overlapping region of counterpropagating primary waves, an interference wave is formed with the total ω _c = ω ₁ + ω ₂ and the difference

frequencies having sharply different propagation speeds: total frequency

and difference

The above dependence for the wave frequency of the total frequency implies the possibility of unlimitedly large (from the standpoint of a "continuous" medium) values of V _c ; in these expressions, c is the speed of sound in the medium. When the medium moves in the pipeline at a speed U, frequency

change by a value proportional to the average over the cross-sectional area of the pipeline, speed:

or - expense

where S is the cross-sectional (radial) cross-sectional area of the pipeline.

 Thus, the flow rate is determined by the change in the frequency of the combination waves relative to the frequency of such waves in a stationary medium.

 The drawing shows a functional diagram of a device that implements the proposed method.

 The device contains a section of the pipeline 1, from the side of the outer surface of which, coaxially with it, two cylindrical emitters of the same cylindrical waves 2, 2 'are installed at a certain distance from each other, connected through signal amplifiers 3, 3' to the outputs of the electric signal generators 4, 4 '; between the emitters, also from the side of the outer surface, a receiver of acoustic signals 5; the latter may be, for example, the same as the emitters. The output of the signal receiver 5 through an amplifier 6 is connected to a frequency mixer 7, which simultaneously receives signals from the generators 4, 4 '. The output of the mixer 7 is connected through a filter 8 with a frequency counter 9. Damping is used - mechanical and using electronic circuits.

На участке 1 трубопровода, между сечениями а и б образуется поле плоских интерференционных волн комбинационных частот:

с волновым вектором

при ω₁ > ω₂. Волны частот

распространяясь в среде трубопровода, возбуждают волны тех же частот

и того же направления распространения в стенке трубопровода. В результате, на устанавливаемый со стороны внешней поверхности трубопровода приемник сигналов 5 будут поступать сигналы частот

которые, после усиления в 6, прохождения через смеситель 7 и фильтр 8, попадают на частотомер 9, регистрирующий разность частот

равную разности между частотами

получаемыми с генераторов 4, 4', и частотами волн, прошедших через среду

(звездочка у символа - зависимость от U).The method of measuring the flow rate of liquid and gaseous media is as follows. From the outputs of the generators 4, 4 ', after amplification of 3, 3', emitters 2, 2 'spaced apart by a distance l emit electrical signals in the form of waves with close frequencies ω ₁ , ω ₂ or pulses with filling at the same frequencies that excite cylindrical waves in the medium filling the pipeline, which in turn generate “collapses” of the fronts of converging cylindrical waves on the longitudinal axis of the pipeline, plane acoustic waves traveling along the pipeline with the same frequencies ω ₁ , ω ₂ and antiparallel wave vectors:

In section 1 of the pipeline, between sections a and b, a field of plane interference waves of combination frequencies is formed:

with wave vector

for ω ₁ > ω ₂ . Frequency waves

propagating in the medium of the pipeline, excite waves of the same frequencies

and the same direction of propagation in the wall of the pipeline. As a result, frequency signals will arrive at the signal receiver 5 installed on the side of the external surface of the pipeline

which, after amplification in 6, passing through a mixer 7 and a filter 8, fall on a frequency meter 9 recording the frequency difference

equal to the difference between the frequencies

obtained from the generators 4, 4 ', and the frequencies of the waves transmitted through the medium

(the asterisk in the symbol is the dependence on U).

в приближенных равенствах которых использовано обычно выполняющееся условие: U•с^-1<< 1.The movement of the medium in the pipeline with a speed U is accompanied by a change in the frequencies of the combination waves:

in approximate equalities of which the usually fulfilled condition is used: U • с ^-1 << 1.

определяемой выражением:

Из (3), по значению

определяется скорость U, а вместе с ней и расход.The change in the frequencies of the combination waves will lead to the appearance in 7 of the uncompensated difference

defined by the expression:

From (3), by value

the speed U is determined, and with it the flow rate.

определяет и чувствительность способа. Из (3) видно, что чувствительность способа чрезвычайно высока даже на частоте

В связи с этим представляется возможным измерение потоков со скоростями течения менее 10^-3 м/с. Для сравнения заметим, что, например, с помощью современных ультразвуковых методов возможно измерение расхода потоков, имеющих скорости не менее 1,0-1,5 м/с.Value

determines the sensitivity of the method. From (3) it is seen that the sensitivity of the method is extremely high even at a frequency

In this regard, it seems possible to measure flows with flow velocities of less than 10 ^-3 m / s. For comparison, we note that, for example, using modern ultrasonic methods, it is possible to measure the flow rate of flows having velocities of at least 1.0-1.5 m / s.

где

определяется с помощью частотомера, а значения

известны.Given the expressions (1-3), the static characteristic of the device, based on the new method, has the form:

Where

determined using a frequency meter, and the values

known.

 The application of the proposed method for determining the flow rate allows to increase the accuracy of measuring the flow rate due to the following main factors: the use of plane waves filling all points of the cross-section of the pipeline and carrying information on velocity values integrated over the cross-sectional area, taking into account any features in the form of a flow velocity profile; ultra-high sensitivity, elimination of additional errors due to complex schemes, due to the extreme simplicity of the principle, electronic flow measurement circuitry, lack of mechanical systems.

Sources of information
1. Kolmakov I.A., Samartsev V.V. RF patent N 2047098, cl. G 01 F 1/66, 1995, bull. thirty.

Claims (1)

 A method for measuring the flow rate of liquid and gaseous media, based on the registration and measurement of vibration frequencies in the medium flow of acoustic waves generated when sounding a transverse cross-section of the flow in the pipeline by acoustic waves due to the action of cylindrical acoustic waves on the flow of emitters, characterized in that they create along the medium flow along the pipeline is opposed by plane acoustic waves with frequencies close to each other and record the values of the total and difference frequencies of the secondary acoustic waves which will determine the amount of flow.