RU2653776C1 - Vortex acoustic flowmeter - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to a measuring technique, and more particularly to a vortex flowmeter designed to measure the flow and quantity of liquids and gases flowing in pipelines and can be used to control, regulate and account for fluid flows. Vortex acoustic flowmeter contains a measuring tube located in the branch pipe across the flow body, a radiator and receiver of ultrasonic vibrations, an ultrasonic frequency signal generator, three frequency dividers into two, two divisors of frequency with a variable coefficient of division, three amplifier-shaper, inverter, two phase detectors, two high-pass filters, low-pass filter, peak detector, two analog-to-digital converters, a multiplexer with two inputs, a microcontroller, an output device.

EFFECT: expansion of the range of permissible phase shift values, increasing the accuracy of measurements during operation over a wide range of temperatures of the controlled medium.

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Description

The invention relates to measuring equipment, and in particular to vortex flowmeters designed to measure the flow rate and the amount of liquids and gases flowing in pipelines, and can be used to control, regulate and account for fluid flows.

Known vortex acoustic flowmeter (US patent No. 4.924.710 C2, IPC G01F 1/32, NKI 78 / 861.238, publ. 05.15.1990) with two electro-acoustic channels, containing a measuring pipe, a streamlined body installed across the stream, two pairs of "emitter-receiver ", a sine wave generator, a phase detector, a pass-pass filter and other nodes. Both pairs of "emitter-receiver" are located directly behind the flow around the opposite walls of the pipeline. A continuous sinusoidal signal of the generator is supplied to the emitters of both pairs of "emitter-receiver". The ultrasonic signals emitted by them cross the flow towards each other and arrive at the receivers. From the outputs of the receivers, the electrical signals modulated in phase after passing through the vortices are fed to a phase detector. The output signal of the phase detector is fed to a band-pass filter that suppresses the carrier frequency, removes the constant component of the phase detector signal, as well as high-frequency noise, the frequency of which lies outside the working range of the vortex frequency. As a result, a signal is generated at the filter output that is close in shape to a sinusoid. The driver amplifier amplifies this signal and generates rectangular pulses from them, the repetition rate of which is equal to the repetition rate of the vortices. The advantage of the flowmeter is the simplicity of the electronic circuit.

The disadvantage of the described vortex-acoustic flow meter is the presence of two electro-acoustic channels, the delay of ultrasonic signals in which, determined by the length of the channel, must be exactly the same. Otherwise (in the presence of geometric asymmetry of the channels), with significant changes in temperature, a drift of the initial phase of the receiving signals is observed, which can lead to loss of operability.

A vortex-acoustic flowmeter with one electro-acoustic channel, selected as a prototype, is free from this drawback (US Patent No. 5,728.947, IPC G01F 1/32, NKI 73 / 861.22, publ. 04/17/1998). The specified flow meter contains a measuring pipe located in the pipe across the stream, the flow around the body, the emitter and the receiver of ultrasonic vibrations, installed diametrically opposite to the flow around the body, the ultrasonic frequency signal generator, the first and second frequency dividers into two, the first and second amplifiers-shapers, inverter, multiplexer with two inputs, phase detector, high-pass filter, low-pass filter, analog-to-digital converter, microcontroller, digital-to-analog converter and others s nodes.

The specified flow meter operates as follows.

From the output of the generator, the signal of the meander type is fed to the input of the first frequency divider into two, the output of which the divided frequency signal is fed to the emitter, which converts it into ultrasonic vibrations propagating from the emitter to the receiver in the form of a traveling wave. The ultrasonic vibrations arriving at the receiver are converted into an electrical signal whose phase with respect to the phase of the signal arriving at the emitter is shifted by

where Δϕ is the phase shift of the reception signal with respect to the excitation signal, ω is the circular frequency of the ultrasonic signal, D is the path length of the ultrasonic signal in the medium equal to the diameter of the measuring tube, C is the speed of sound in a stationary medium, V _≈ is the average along the path of the ultrasonic signal the value of the variable component of the projection of the flow velocity V _l on the direction of propagation of the ultrasonic signal:

where Ω is the circular frequency of vortex formation, V is the average flow velocity over the cross section, m <1 is the modulation coefficient, which depends on the size and intensity of the vortices, t is the time.

A sinusoidal signal from the output of the receiver is fed to the input of the first amplifier-driver, which is converted into rectangular pulses supplied to the first input of the phase detector. From the output of the generator, the signal also goes to the input of the inverter, the output of which is connected to the first input of the multiplexer, and also directly to the second input of the multiplexer. Depending on the magnitude of the control signal received from the microprocessor, either the generator output signal or the inverse signal from the inverter output passes to the multiplexer output. The output signal of the multiplexer is fed to the input of the second frequency divider by two. The signal from the output of the second divider into two, depending on which signal passes to the output of the multiplexer, either coincides in phase with the output signal of the first frequency divider by two, or is 90 ° out of phase with respect to it. The signal from the output of the second divider is fed to the second input of the phase detector and is reference to the output signal of the first amplifier-former. The phase detector is designed as an exclusive OR. The ripple voltage at the output of the phase detector is the sum of the constant and variable components. The constant component is determined by the phase advance of the ultrasonic signal without taking into account the influence of vortices Δϕ ₌ :

The constant component is extracted by a low-pass filter, converted into a digital code by an analog-to-digital converter and supplied to one of the inputs of the microcontroller, where its value is analyzed. If the value of the constant component approaches zero or the maximum value, this means that Δϕ ₌ approaches the singular points of the phase detector characteristic 0 ° or 180 °. In this case, the microcontroller generates a control signal for the multiplexer, which connects its output to another input. In this case, the phase of the reference signal abruptly changes by 90 °, the constant component of the output voltage of the phase detector abruptly changes to a value equal to half the maximum, and the normal operation of the phase detector is restored.

The variable component of the output voltage of the phase detector is proportional to the variable component of the phase shift Δϕ _≈ :

It is extracted using a high-pass filter and fed to a second amplifier-driver, which forms rectangular pulses. These pulses are fed to another input of the microcontroller, which converts the frequency of the signal into a digital code, which is input to the digital-to-analog converter. A digital-to-analog converter converts the code into an electrical signal (voltage or current) proportional to the measured flow rate, which is the output value of the flowmeter

The described vortex acoustic flow meter has the following disadvantages:

1. The permissible phase shift range Δϕ _{≈ is} limited by ± π / 2. Meanwhile, the range of variation of the flow velocity is usually not less than 50: 1, the diameter range of the measuring pipe for a number of industrial series of flowmeters is 12: 1 (from 25 to 300 mm), the range of variation of the speed of sound is ~ 1.5: 1, t. e. the range of variation of the square of the speed of sound is 2.25: 1. In addition, in the range (0; π), the signal amplitude equal to twice the amplitude should fit. It follows that the total possible range of phase shift of the reception signals for all sizes of a number of flowmeters is at least 50 × 12 × 2.25 × 2 = 2700: 1. It is impossible to provide measurements in this range using the same frequency of the probing signal, since usually the frequency of the probing signal is of the order of (1 ... 2) MHz, and when measuring in large diameter pipelines it is possible that the phase shift exceeds π.

To reduce the magnitude of the phase shift, it is possible to use different frequencies ω - the larger the diameter D, the smaller the frequency ω should be. The disadvantage of this technical solution is the need to have several options for the execution of electronic units and ultrasonic emitters, which reduces the degree of unification of flow meters and, as a result, increases their cost.

2. When the multiplexer is switched to the input of the phase detector, another reference signal (90 ° shifted relative to the previous one) is connected, which is accompanied by an abrupt change in the level of the constant component of the output signal of the phase detector. A transient process occurs, accompanied by the passage of a certain number of output pulses. In some cases, for example, with accurate measurement of small volumes, such a failure is unacceptable.

The expected technical effect of the invention is to expand the scope and increase the accuracy of measurements.

This effect is achieved by the fact that in a vortex-acoustic flowmeter containing a measuring pipe located in the pipe across the stream, the flow body, the emitter and the receiver of ultrasonic vibrations are installed diametrically opposite behind the body flow, the ultrasonic frequency signal generator, the first and second frequency dividers into two, the first and second driver amplifier, inverter, first phase detector, first high-pass filter, low-pass filter, first analog-to-digital converter, multiplexer two inputs, a microcontroller, an output device additionally introduced first and second frequency dividers with a variable division factor, a third frequency divider into two, a third power-generator, a second phase detector, a second high-pass filter, a peak detector, a second analog-to-digital converter.

The input of the first frequency divider with a variable division coefficient is connected to the output of the first amplifier-driver, and the output is connected to the first inputs of the first and second phase detector, the input of the second frequency divider with a variable division coefficient is connected to the output of the master oscillator, and the output is connected to the inverter input and the input of the second frequency divider into two.

The control inputs of frequency dividers with a variable division coefficient are connected to the same output of the microcontroller, the inverter output is connected to the input of the third frequency divider by two, the outputs of the second and third frequency dividers by two are connected to the second inputs of the first and second phase detector, the output of the second phase detector connected through a high-pass filter to the third driver amplifier, the outputs of the second and third amplifier drivers are connected to the information inputs of the multiplexer, controlling the input and a multiplexer output connected to the microcontroller, the peak detector input coupled to an output of the first highpass filter and the output of the peak detector through a second analog-to-digital converter connected to a microcontroller, wherein the frequency dividers of the variable division ratio division ratios are the same.

The invention is illustrated in the drawing, on which are presented: in FIG. 1 is a functional diagram of a flow meter; in FIG. 2 - illustration of the normal operation of the phase detector; in FIG. 3 is an illustration of the occurrence of distortions in the output signal of a phase detector that occurs when a direct component of the phase shift hits a neighborhood of points n⋅π, n = 0, 1, 2, 3, ....

The vortex-acoustic flow meter (Fig. 1) contains a measuring pipe 1, a flow body 2, an emitter 3 and a receiver 4 of ultrasonic vibrations, a master oscillator 5, first 6, second 7 and third 8 frequency dividers into two, first 9, second 10 and third 11 amplifiers rectangular pulse shapers, inverter 12, first 13 and second 14 frequency dividers with variable division ratio, first 15 and second 16 phase detectors, first 17 and second 18 high-pass filters, low-pass filter 19, peak detector 20, first 21 and second 22 analog-to-digital conversion Indicators, multiplexer for two inputs 23, microcontroller 24, output device 25.

The flow meter operates as follows.

With the passage of fluid through the measuring pipe 1 behind the flow body 2, a Karman vortex path is formed, in which periodic fluctuations in the local flow velocity occur with a frequency equal to the vortex formation frequency. Fluctuations in speed are converted into electrical vibrations by probing the vortex track with an ultrasonic signal. To do this, from the generator 5 to the first frequency divider for two 6 receives a signal in the form of rectangular pulses of frequency 2ω:

where H (x) is the Heaviside function: H (x) = 1 for x> 0 and H (x) = 0 for x <0 [4]. The amplitude of the signal is hereinafter referred to everywhere as U _m .

From the output of the frequency divider by two 6 to the emitter 3 receives a frequency signal ω:

The emitter 3 converts the electrical signal (6) into an ultrasonic probe signal, which propagates across the stream, passes through the vortex track and enters the receiver 4. When passing through the vortices, the phase of the ultrasonic signal receives an additional increment - positive or negative - depending on the sign of the projection of the velocity vector vortex to the direction of propagation. The time delay of the ultrasonic signal in the stream Δτ is:

where V _≈ is expressed by formula (2).

The receiver 4, the ultrasonic signal is converted into an electrical signal:

The signal (8) from the output of the receiver is fed to the input of the first amplifier-driver 9, at the output of which a sequence of rectangular pulses of frequency ω is formed:

From the output of the first amplifier-driver 9, the signal (9) is fed to the input of the first divider 13 with an integer division coefficient N = 1, 2, 3, ..., at the output of which a divided frequency signal ω / N with a duty cycle of 2 is formed:

The signal (5) of the generator 5 of frequency 2ω is also supplied to the input of the second divider 14 with a division coefficient N (equal to the division coefficient of the first divider 13). The output signal of the divider 14 with a frequency of 2ω / N

arrives at the input of the second frequency divider by two 7 and the input of the inverter 12, the output of which is connected to the input of the third frequency divider by two 8. At the outputs of the frequency dividers 7 and 8, frequency signals ω / N with a duty cycle of 2 are shifted in phase by 90 °:

The signals (12) and (13) from the outputs of the dividers 7 and 8 are fed to the first inputs of the phase detectors 15 and 16, the second inputs of which receive a signal (10) from the output of the divider 13. A phase detector 15, constructed, for example, according to the balanced modulator , multiplies the signal (10) by the signal (12). In this case, components are formed whose arguments are equal to the sum and phase difference of these signals. The component with the sum of the phases gives a signal with a frequency of 2⋅ω / N, which is filtered by phase detectors. As a result, a voltage is generated at the output of the phase detector 15

where the braces {x} denote the fractional part of the number x, U _π is the maximum output voltage of the phase detector corresponding to the phase shift π, proportional to the phase difference of the signals (12) and (10):

Similarly, the phase detector 16 multiplies the signal (10) by the signal 13), as a result of which a voltage is generated at the output of the phase detector 16

proportional to the phase difference of the signals (13) and (10):

From the expressions (15) and (17) it follows that each of the phase differences Φ ₁ and Φ ₂ is the sum of a slowly varying (due to a change in the operation of the flowmeter sound velocity C, which is a function of temperature) component and a component oscillating due to the vortices ( the dependence of the oscillating component on the speed of sound can be neglected). The constant part of the difference Ф ₁ is equal to the phase incursion in a stationary medium plus an additional shift π / 2:

The constant part of the difference Ф ₂ is equal to the phase incursion in a stationary medium:

The phase shift π / 2 corresponds to the voltage U _π / 2, i.e. voltage U _PD1 and U _PD2 differ from each other by the value of U _π / 2.

The variable components of the phase differences f ₁ and f _{2 are the} same and are:

A comparison of expressions (4) and (20) shows that due to frequency division, the variable component of the phase shift decreases N times.

The formation of the output voltages of the phase detectors 15 and 16 occurs in accordance with the characteristic, which for the balanced modulator has the form shown in FIG. 2. This characteristic is ambiguous, it is unique on the segments (n⋅π; (n + 1) ⋅π), n = 0, 1, 2, 3, ....

For normal operation of the vortex-acoustic flowmeter, it is necessary that during the measurement phase shift Ф ₁ or Ф ₂ does not go beyond the interval (n⋅π; (n + 1) ⋅π), as shown in FIG. 2. Otherwise, signal distortions occur that can disrupt the flowmeter, see FIG. 3.

The output signals of the phase detectors 15 and 16 are fed to the input of the low-pass filter 19, as well as to the inputs of the high-pass filters 17 and 18.

Using a low-pass filter 19, a constant voltage is allocated:

The maximum voltage U _π corresponds to a phase shift π. The voltage U of the _{low-pass filter is} supplied to the input of an analog-to-digital converter 21, which converts it into a digital code supplied to the first input of the microcontroller 23.

Using the first and second high-pass filters 17 and 18, the variable components of the signals (14) and (16) are extracted:

Using the second and third amplifiers-shapers 10 and 11, the variable components of the signals are converted into rectangular pulses, which are fed to the inputs of the multiplexer with two inputs 23, the output of which is connected to input 2 of the microcontroller 24, and the control input to the output 3 of the microcontroller 24. In addition , the output signal of the first highpass filter 17 is input to a peak detector 20 which converts the signal amplitude at constant voltage U _DD, which in turn is converted to analog-to-digital pr 22-forming a digital code supplied to the fourth input of the microcontroller 23.

The microcontroller analyzes the magnitude of the voltage U _LPF and U _PD coming from the outputs of the analog-to-digital converters 21 and 22, as follows.

Analysis of voltage U _LPF . If the voltage U _LPF satisfies the condition

this means that the phase shift is in the working range of the phase detector 15. In this case, the microcontroller 24 supplies the control signal to the multiplexer 23, which connects the output signal of the amplifier-shaper 10 to the input 2 of the microcontroller 24. The microcontroller 24 converts the frequency of the output signal of the amplifier-shaper 10 into a digital code that is supplied to the output device 25.

If the conditions are met

or

this means that the constant component of the phase shift approaches the singular points of 0 ° or π. In this case, under normal conditions, the second phase detector 16 operates, and the microcontroller 24 supplies the multiplexer 23 with such a control signal, which connects the output signal of the amplifier-former 11 to the input 2 of the microcontroller 24.

In this way:

1) the input 2 of the microcontroller 24 always receives a signal generated with the participation of a normally working phase detector;

2) when switching the multiplexer 23 there is no transient process and the accompanying additional error, since with the help of the multiplexer 23 one of the constantly existing pulse signals is connected to the input of the microcontroller 24.

Analysis of voltage U _PD . If the magnitude of the voltage U _PD exceeds the value corresponding to the amplitude of the phase shift, for example π / 5, from the control output 5 of the microcontroller 24 to the control inputs of the dividers 12 and 13 receives a code signal, according to which the division coefficient is increased by one unit. In this case, the amplitude of the variable component decreases accordingly. Further, the measurement process continues, and if the phase shift amplitude again exceeds π / 5, the division coefficient increases by one more unit, etc. Thus, the value of the frequency division coefficient N is automatically set such that at the maximum flow rate Q = Q _{max the} amplitude of the phase oscillations of the signals at the outputs of the phase detectors 15 and 16 does not exceed 2π / 5, i.e. the amplitude of phase oscillations did not exceed π / 5:

where S is the cross-sectional area of the measuring pipe.

From here we obtain the value of the frequency division coefficient N:

where ƒ = ω / 2π.

The frequency ƒ of the ultrasonic probe signal is usually (1 ... 2) MHz. We calculate the approximate value of the maximum division coefficient N. For this, we consider a flowmeter with a maximum nozzle diameter D = 300 mm (S = 7.07 dm ² ), ƒ = 2⋅10 ⁶ Hz, C = 1.17⋅10 ³ m / s ( working fluid - gasoline), Q _max = 2545 m ³ / h = 0.707 m ³ / s. Substituting the numerical values of the quantities in the formula (27), we obtain:

The nearest integer is 6. Thus, the range of variation of the division factor should be approximately 1: 6.

From the foregoing, it follows that, in comparison with the prototype device, the claimed device provides:

1) the optimal use of the working range of the phase detector for any amplitude of the variable component of the phase difference of the receiving and reference signals (due to modulation of the ultrasonic signal by vortex structures and carrying useful information) due to preliminary division of the frequency of these signals with the automatic setting of such a division coefficient at which at the maximum consumption, the amplitude of the phase difference of the receiving and reference signals is approximately 2π / 5;

2) measurement of flow and quantity without loss of accuracy in a wide range of changes in the speed of sound in a controlled environment C due to the exclusion in principle of gaps in the output pulses during changes in the reference signal that occur during measurements during operation, for example, in a wide temperature range.

Tests carried out at the flowmeter test bench showed that the application of the proposed technical solution provides the optimal mode of operation of the vortex-acoustic flowmeter with a measuring tube diameter of 25 to 300 mm for any value of sound velocity and temperature of the controlled medium.

LITERATURE

1 US patent No. 4.924.710 C2, IPC G01F 1/32, NKI 78 / 861.238, publ. 05/15/1990.

2 US Patent No. 5,728.947, IPC G01F 1/32, NKI 73 / 861.22, publ. 04/17/1998.

3 Volkov I.K., Kanatnikov A.N. Integral transformations and operational calculus: Textbook. for universities / Ed. V.S. Zarubina, A.P. Krishchenko. - 2nd ed. - M.: Publishing House of MSTU. N.E. Bauman, 2002 .-- p. 228.

Claims (1)

A vortex-acoustic flow meter containing a measuring pipe located in the pipe across the stream of the flow around the body, the emitter and receiver of ultrasonic vibrations installed diametrically opposite behind the body of the flow, an ultrasonic frequency signal generator, the first and second frequency dividers into two, the first and second amplifier driver, inverter, first phase detector, first high-pass filter, low-pass filter, first analog-to-digital converter, multiplexer with two inputs, microcontroller, output nth device, characterized in that it additionally includes the first and second frequency dividers with a variable division ratio, a third frequency divider into two, a third driver amplifier, a second phase detector, a second high-pass filter, a peak detector, a second analog-to-digital converter, the input of the first frequency divider with a variable division coefficient is connected to the output of the first amplifier-driver, and the output is connected to the first inputs of the first and second phase detector, the input of the second frequency divider with a variable coefficient the division factor is connected to the output of the master oscillator, and the output is connected to the inverter input and to the input of the second frequency divider by two, the control inputs of the frequency dividers with a variable division coefficient are connected to the same output of the microcontroller, the inverter output is connected to the input of the third frequency divider by two , the outputs of the second and third frequency dividers into two are connected to the second inputs of the first and second phase detector, the output of the second phase detector is connected through a high-pass filter to the third amplifier amplifier Atelier, the outputs of the second and third amplifiers-drivers are connected to the information inputs of the multiplexer, the control input and output of the multiplexer are connected to the microcontroller, the input of the peak detector is connected to the output of the first high-pass filter, and the output of the peak detector through the second analog-to-digital converter is connected to the microcontroller, when In this case, frequency dividers with a variable division coefficient have the same division factors.

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