RU2193208C2 - Ultrasonic method measuring current speed (versions) - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method is used to measure current speed in river, open bed of washing gallery and tube of large inner diameter. Amplitude modulation of undamped harmonic ultrasonic sinusoidal wave f_c with signal of frequency f_м, is carried out, propagation/reception of amplitude-modulated signal is conducted and wave of amplitude modulation is used to measure propagation tie of ultrasound. According to second variant phase difference is determined. In this case amplitude modulation of ultrasonic wave by signal with frequency f_м determined beforehand is carried out. If phase difference between ultrasonic waves propagated in directions coinciding with current speed or opposite to it exceeds π radian then transmission/reception of amplitude-modulated signals is conducted, phase difference between amplitude-modulated signals is measured. Then phase difference between ultrasonic waves is measured again. EFFECT: increased authenticity and measurement accuracy and expanded application field. 4 cl, 6 dwg

Description

The technical field to which the invention relates.
The invention relates to the development of a method for measuring the flow velocity using an ultrasound beam to calculate the flow rate of an open channel of a large river or a wash gallery and the flow rate of liquid and gas in a pipe of large internal diameter.

BACKGROUND OF THE INVENTION
The main part of the modern well-known ultrasonic flow measurement system for a large open channel of a washing gallery and a pipe of large internal diameter is designed to measure the flow rate of liquid and gas, so this system is usually called a "flow meter".

 Most flow measurement systems have been proposed for measuring the flow velocity using a method for measuring the flow velocity based on the difference in ultrasound propagation times.

As shown in figure 1, the system for measuring the flow velocity based on the difference in the propagation times of ultrasound has the following composition: transducers 1 and 2 for transmitting / receiving ultrasonic waves are installed at an angle α and face each other. The switching circuit 3 is configured to connect the transducers 1 and 2 to the inputs of the transmission and reception circuits, for example, an ultrasonic pulse generator 4 and an amplifier 5 of the received ultrasonic signal. The pulse shaping circuit 6 receives the amplified signal and gives it the shape of a pulse signal of shorter duration. The device 7 measuring time intervals measures the propagation time t ₁ and t ₂ at a distance L of the interval from the moment of transmission to the moment of reception. The arithmetic-logic unit 8 calculates the flow rate based on the expression (1).

That is, the propagation time t ₁ is measured, during which the ultrasound beam passes from the transducer 1 to the transducer 2 (as shown in FIG. 1). Conversely, the propagation time t ₂ is measured, during which the ultrasonic beam passes from the transducer 2 to the transducer 1. These measured times are determined as follows:
t ₁ = L / (C + Vcosα);
t ₂ = L / (C-Vcosα).

It turns out that the difference in propagation times (Δt = t ₂ -t ₁ ) can be represented as follows:
Δt = 2LVcosα / C ² . (1)
In this case, C is the speed of sound in a liquid or gas, L is the interval between transducers 1 and 2, and V is the average flow velocity in the interval L.

The flow velocity V is derived from expression (1) in the following form:
V = ΔtC ² / 2Lcosα. (2)
This can be called the “Method of measuring the flow velocity based on the difference in propagation times” because the flow velocity V is proportional to the difference Δt of the propagation times. It seems that the method of measuring the flow velocity based on the difference in the propagation times is related to the speed of sound, since in expression (2) there is a C ² term square of the speed of sound. The form of this expression is as if it is necessary to measure the term C ^{2 of the} square of the speed of sound. The square of the speed of sound is represented as follows:
C ² = L ² / t ₁ t ₂ .

Member C ^{2 of the} square of the speed of sound is substituted into expression (2) to obtain the following final expression for measuring the flow velocity:
V = (L ² / Lcosα) [(t ₂ -t ₁ ) / t ₁ • t ₂ ] = (L ² / 2d) [(t ₂ -t ₁ ) / t ₁ • t ₂ ]. (3)
Then, the flow velocity is obtained by measuring only the ultrasound propagation times t ₁ and t ₂ and calculating expression (3), since L ² / 2d = const.

 Typical well-known technical solutions are described in US patent 5531124, issued July 2, 1996, Japan patent 2676321, issued July 25, 1998, "Guide to ultrasonic flow measurement and device for its implementation" and in the "Description of the ultrasonic flow meter model" UEF-2100C " (UF-2100C) manufactured by Ultraflux Co. (Ultraflux Co.).

 The method of measuring the flow velocity based on the difference in propagation times has a huge advantage in that it is easy to measure the flow velocity, which illustrates expression (3), even though the speed of sound varies greatly in a liquid. That is, although it seems that expression (3) is related to the square of the speed of sound, but, according to the derivation method of the expression for measuring the flow velocity, this term is in principle not related to the flow velocity.

For example, the difference between the inverse values of the propagation times t ₁ and t ₂ get in the following form:
(1 / t ₁ ) - (1 / t ₂ ) = 2Vcosα / L.

где d = L/cosα.
В результате, полученное выражение идентично выражению (3).Members of the speed of sound cancel each other out. Therefore, the flow velocity V has the following form:

where d = L / cosα.
As a result, the resulting expression is identical to expression (3).

It has the great advantage that the method of measuring the flow velocity based on the difference in propagation times is not associated with a wide variation in the speed of sound C in a fluid. But the application of the method of measuring the flow velocity based on the difference in propagation times is limited. For example, when the propagation distance L is very small and / or the flow velocity V is very low, it is very difficult to accurately measure the flow velocity. If L = 0.1 m / s, α = 45 ^o and С≈1500 m / s, then Δt≈3.14-10 ^-9 s.

If you intend to measure a very small time difference in the error range of 1%, the absolute error of measuring the time difference should not exceed 3-10 ^-11 s. A time difference measurement based on a similar methodological technique requires a relatively sophisticated device for measuring the time interval. In addition, the device for fixing the moment of transmission / reception of ultrasonic pulses must be very reliable and accurate. As mentioned below, a method of measuring the flow velocity based on the difference in the propagation times creates many problems when measuring the gas flow velocity in a pipe or the horizontal flow velocity in a gallery or river.

 In addition to the method for measuring the flow velocity based on the difference in propagation times, a method for measuring the flow velocity based on the phase difference of ultrasound is also well known. For example, there is the publication of the Danish Patent Application Laid-Open DE 19722140 of November 12, 1997 and the publication of the Japanese Patent Laid-open Application of April 24, 1998, entitled "Multichannel Flow Measurement System".

2A and 2B show a typical configuration of a flow velocity measurement system based on a phase difference. Ultrasonic transducers 1, 1 'and 2, 2' are located so that they are facing each other. A sine wave generator 9 generates a sine wave having a frequency f. The phase shifter 10 controls the phase of the received ultrasonic signals. The amplifier 11 amplifies the received signals from the phase shifter 10 and the converter 1 '. The phase difference discriminator 12 measures the phase difference between the received phase signals. During operation of the sine wave generator 9, the transducers 2 and 2 'transmit ultrasonic waves with the same phase. At this moment, the phase signals received by the receiving transducers 1 and 1 'have the following form:
φ ₁ = 2πf • t ₁ + φ ₀ ;
φ ₂ = 2πf • t ₂ + φ ₀ ,
Where
t ₁ = L / (C-Vcosα);
t ₂ = L / (C + Vcosα),
φ ₀ is the initial phase with which the ultrasonic wave propagates first. Therefore, the phase difference Δφ between the received signals has the following form:
Δφ = φ ₁ -φ ₂ = 2πfΔt = 2πf (2LVcosα / C ² ). (4)
Here, the flow velocity has the following form:
V = (ΔφC ² ) / (4πfLcosα). (5)
The method for determining the phase difference has signs that ultrasonic waves can propagate continuously, and the phase difference Δφ is proportional to the frequency f, in contrast to the method for determining the difference in propagation times. Therefore, even if L and V are very small, when choosing a higher ultrasonic frequency, the phase difference becomes larger, so that the measurement of the phase difference is convenient and accurate.

 In addition, if the L value is relatively large, the attenuation coefficient is very small with the passage of the ultrasonic pulse, since the transmission / reception of ultrasonic undamped harmonic waves occurs. In addition, even if the amplitude of the received signal is very pulsating, it is possible to provide sufficient amplification of the received signal, because the moment of reception is not measured. With this method, you can use the automatic gain control circuit. This means that when measuring the phase difference there are no problems at all. But the method of determining the phase difference is preferably used provided that the speed of sound C is almost unchanged, or in the case when some other means measures the speed of sound C. For example, to measure gas flow, the speed of sound in a gas can be easily calculated provided that a pressure gauge and a thermometer are installed in the pipe.

 As mentioned above, the great advantage of the method involving determining the difference in the propagation times of ultrasound is that it can be used even in a situation where the speed of sound in a fluid varies significantly. But if the interval L between the transducers becomes longer, the following problems arise due to the transmission / reception of the ultrasonic pulse.

 Firstly, an ultrasonic pulse has a larger attenuation coefficient than a sine wave, due to the presence of sufficient harmonic components or overtones in it. If the propagation distance L of the ultrasound becomes larger, it is difficult to receive the transmitted ultrasonic wave, and the received pulse takes the form of a bell due to a serious attenuation problem. For all these reasons, it is impossible to increase the intensity of the ultrasonic wave, which can be further adjusted. If the intensity becomes larger, the phenomenon of cavitation occurs in the river, so that the ultrasonic wave does not propagate. In particular, when decreasing the pulse frequency to reduce the attenuation coefficient, the ultrasound intensity also decreases, which causes the occurrence of cavitation.

 Secondly, the ultrasonic pulse during transmission does not decay only at a distance L, and the amplitude of the ultrasonic wave pulsates strongly, as a result of which the ultrasonic wave is scattered and reflected due to various eddy currents, changes in the concentration of floating particles, changes in water temperature, etc. in the open channel of the washing gallery. Sometimes it happens that the reception of an ultrasonic wave does not occur.

 When measuring the flow velocity in a gas, the attenuation coefficient of an ultrasonic pulse is greater than the attenuation coefficient of an ultrasonic pulse in a liquid. The strong attenuation and pulsation of the ultrasonic pulse create many errors in fixing the moment when the ultrasonic pulse arrives. Thus, the error in measuring the flow velocity increases.

 For these reasons, the propagation distance L of the ultrasound is limited by the distance at which the ultrasound pulse is transmitted / received, and the flow rate is measured using a method involving determining the time difference. Thus, serious obstacles arise when measuring the flow velocity in the open channel of a large washing gallery or river and a large pipe.

If the method involving determining the phase difference is used to measure the flow velocity, then the corresponding attenuation coefficient is reduced by two or three times compared with the attenuation coefficient when using an ultrasonic pulse, because the transmission / reception of ultrasonic undamped harmonic waves (sine waves) occurs. In addition, the method of determining the phase difference is not associated with amplitude ripple, since it is not associated with fixing the moment when an ultrasonic pulse arrives, but involves measuring the phase difference between two sinusoidal waves. However, the use of a method involving the determination of the phase difference is limited. If the phase difference Δφ between two sinusoidal waves is nπ + β, a conventional device for measuring the phase difference cannot determine n (1, 2, 3 ...). If the ultrasonic propagation distance L or the flow velocity V increases, Δφ becomes greater than π. For example, if you intend to measure the gas flow in a pipe having an internal diameter Φ equal to 300 mm, the average flow velocity V of the gas, determined in a certain cross section, is usually 10 ~ 30 m / s. Further, under the assumption that the speed of sound C is 400 m / s, the ultrasonic frequency is selected at 400 kHz to ensure that the noise frequency band is exceeded, and the angle α is 45 ^o , the varying phase difference range Δφ is as follows:
Δφ = 9.42 ~ 28.26 rad≈ (2π + 0.998π) ~ (8π + 0.995π).

That is, Δφ> π.
If L = 10 m, V = 3 m / s, f = 200 kHz and C = 1500 m / s in a relatively small open channel, the phase difference Δφ is as follows:
Δφ≈16.746 rad = 5π + 0.33π> π.
Thus, the method of determining the phase difference cannot be used when measuring the flow velocity in a relatively small open channel. In other words, the method of determining the difference in propagation times is advantageous when used in a situation where the speed of sound varies widely. But it has the disadvantage that if the interval L, at which the flow velocity is measured, increases, the ultrasonic pulse becomes unstable, since this ultrasonic pulse, as a rule, damps due to its own properties during transmission / reception.

 The method of determining the phase difference has the advantage that the attenuation coefficient is relatively small and it is easy to process the received signal, since there is a transmission / reception of a sine wave. But if the phase difference exceeds π radians, as a result of which the interval L and the flow velocity V become larger or the speed of sound becomes smaller, it is impossible to measure the flow velocity on the basis of a method involving determining the phase difference. In addition, the method of determining the phase difference has the disadvantage that it is necessary to separately measure the speed of sound.

 The objective of the invention is to develop an ultrasonic method for measuring the flow velocity, designed to measure the flow velocity based on the method of determining the difference of propagation times for measuring the flow velocity, and the method of determining the phase difference, smoothly, if the interval L, which measure the flow velocity is relatively high, for example, if the horizontal average flow velocity is measured in the open channel of the wash gallery or in the river.

 Another objective of the invention is to develop an ultrasonic method for measuring the flow velocity, designed to measure the flow velocity based on the ultrasonic method for determining the difference of propagation times for measuring the flow velocity, and the method for determining the phase difference smoothly if the measurement interval L is horizontal the average flow velocity is relatively large, for example, if the gas flow velocity is measured in a pipe with a relatively large internal diameter a.

 Another objective of the invention is to develop an ultrasonic method for measuring the speed of the stream, designed to measure the speed of the stream based on the ultrasonic method for determining the difference in propagation times for measuring the speed of the stream, and a method for determining the difference in phase, smoothly, if measure the speed gas or liquid in a pipe of relatively large internal diameter.

 And another objective of the invention is to develop an ultrasonic method for measuring the flow velocity, designed to measure the flow velocity on the basis of the ultrasonic method for determining the difference of propagation times for measuring the flow velocity, and a method for determining the phase difference smoothly if the flow velocity relatively large, and the speed of sound is relatively small.

Summary of the invention
According to the invention, an ultrasonic flow velocity measurement method based on a method for determining a propagation time difference for measuring a flow velocity without transmitting / receiving an ultrasonic pulse includes the steps of performing amplitude modulation of a carrier undamped harmonic ultrasonic sine wave into a lower frequency and transmitting amplitude-modulated signals every time when measuring the propagation time of ultrasound, carry out a demodule iju received signals carry detection or discrimination of the amplitude-modulated signal and measuring a time interval between the moments of amplitude modulation of the propagating wave and demodulation of the received amplitude modulated signal.

 An ultrasonic method for measuring the flow velocity, based on a method involving determining a phase difference independent of the speed of sound, includes steps for amplitude modulating the ultrasonic wave at a lower frequency if the phase difference between the ultrasonic waves transmitted in the opposite direction to the flow velocity exceeds π radians, going beyond the measurement range of a conventional discriminator of the phase difference, and becomes equal to mπ + β, and the transmission / reception of the amplitude-modulated signal la, measure the phase difference between the amplitude-modulated signals and between the transferred ultrasonic waves and get m, and provide a very accurate measurement of the phase difference between the transferred ultrasonic waves.

Brief Description of the Drawings
Now the invention will be described in detail with reference to the accompanying drawings, where
FIG. 1 is a schematic block diagram illustrating a system for measuring a flow velocity based on a difference in ultrasound propagation times in accordance with the prior art,
FIG. 2A and 2B are a schematic block diagram illustrating a system for measuring a flow velocity based on a phase difference of ultrasound in accordance with the prior art,
FIG. 3 is a timing chart illustrating processing according to a method for measuring a flow velocity based on a difference in ultrasound propagation times in accordance with the invention,
FIG. 4 is a schematic block diagram illustrating a system for measuring a flow velocity based on a difference in ultrasound propagation times in accordance with the invention,
FIG. 5 is a schematic block diagram illustrating a system for measuring a flow velocity based on an ultrasound phase difference in accordance with the invention,
FIG. 6 is a schematic block diagram illustrating a system for measuring a flow velocity based on an ultrasound phase difference in accordance with another specific embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
First, with reference to the accompanying drawings, a detailed explanation will be given of a method for measuring the flow velocity based on the difference in the propagation times of ultrasound in accordance with the invention.

FIG. 3 is a flowchart illustrating a method for measuring flow velocity. It is known that the frequency f _{with an} ultrasonic carrier is usually chosen taking into account the frequency band of the noise generated in the fluid flow, reliability with respect to the radiation pattern of the ultrasonic transducer, the attenuation coefficient of ultrasound in the fluid, etc.

When measuring the flow velocity, the amplitude modulation of the selected ultrasonic carrier f _s (Fig. 3, VI) is carried out at a frequency f _m (Fig. 3, I), which is less than the frequency f _s , over a period of τ ₂ (Fig. 3, V ), and then propagation in the direction coinciding with the flow velocity or opposite to it. And, considering the predefined moment of amplitude modulation as the starting point, measure the time from the starting point to the appointed moment of the frequency or signal f _{m of} amplitude modulation during the propagation / reception of the amplitude-modulated ultrasonic wave over a constant interval L, and the received signal is demodulated. The time is determined in the form of times t ₁ and t _{2 the} propagation of ultrasound propagated in the direction coinciding with the flow velocity or opposite to it. In other words, an amplitude-modulated ultrasonic wave acts as a mark signal for measuring the propagation time of an ultrasonic wave. And since the ultrasonic wave is a kind of sine wave that continuously propagates and undergoes amplitude modulation for a constant time interval for measuring the flow velocity, the ultrasonic frequency band is f _s ± f _m and is much narrower than the frequency band of a shorter ultrasonic pulse, so that the attenuation coefficient of this wave becomes smaller. And even if the attenuation coefficient undergoes too small changes, the processing of the received signal is simple and does not affect the measurement of propagation time.

But if the amplitude modulation of wave f _{with an} ultrasonic carrier into the signal f _m amplitude modulation is carried out, it is necessary to carry out amplitude modulation with the same phase as the phase of the signal f _m amplitude modulation, for example, with a zero phase, as shown in Fig. 3, V. When the amplitude-modulated voltage is applied to the ultrasonic transducer, some type of ultrasonic wave equivalent to the applied voltage does not propagate, but the shape is distorted in the first half-period of the modulated ultrasonic wave. Moreover, the signal obtained by receiving / demodulating the amplitude-modulated ultrasonic wave does not correspond to the waveform f _m amplitude modulation. With these features in mind, the amplitude-modulated signal supplied to the ultrasonic transducer is introduced into the demodulator for demodulation and the signal f _{m of the} amplitude modulation is detected from the demodulation signal and the moment when the first period of the modulation signal passes through the zero potential is recorded using the zero-crossing discrimination scheme . It should be noted here that the fixed moment is considered the starting point for measuring the propagation time of ultrasound, as shown in FIGS. 3, VII and VIII.

Similarly, the received amplitude-modulated signal is also demodulated using a demodulator, as emphasized above, the signal f _{m of the} amplitude modulation is detected from the demodulation signal, and then the moment is recorded when the first period of the modulation signal passes through the zero-point intersection, performing the function of the end-time signal interval, as shown in figure 3, X and XI.

 As described above, the accuracy of measuring the propagation time of ultrasound can be significantly improved, as a result of which only one demodulator demodulates the transmitted / received signals, and the moments when the first period of the demodulation signal passes through the zero-point intersection are used as signals for the beginning and end of the measurement of the time interval .

As shown in FIGS. 3, VIII and XI, it is inappropriate to use the moments when the one and a half period of the signal f _m amplitude modulation, and not the first half period, pass through the zero-point intersection as signals of the beginning and end of the time interval. Of course, in a demodulator, amplifier, zero-level crossing circuit, etc. a delay time occurs, but it is not necessary to compensate for this delay time, since the same delay time arises in the system every time the flow velocity is measured.

And therefore, the signal f _m amplitude modulation must be fixed under the following conditions.

The first condition is that the signal f _m amplitude modulation is much larger than the frequency f _{p the} ripple attenuation, for example, f _m >> f _p . An ultrasonic wave has a damping coefficient that varies due to many factors during propagation in a fluid. The fact of changing the attenuation coefficient is used to make the ultrasonic wave amplitude-modulated. Thus, the amplitude modulation frequency f _m must be greater than the attenuation ripple frequency f _p with which the attenuation coefficient pulsates and which is not the frequency of the noise generated in the fluid. The attenuation pulsation frequency f _p is small and usually does not exceed 100 Hz.

The second condition is that the carrier period must be contained more than 20 times in the period of amplitude modulation, for example, f _m ≤f _c / 20. This condition concerns the amplitude modulation of the carrier f _c , in which the phase of the carrier f _c at the starting point of the amplitude modulation is not always the same even when performing the amplitude modulation of the carrier f _c at the zero-point intersection, as shown in Fig. 3, V. Therefore, the amplitude-modulated the ultrasonic wave contributes to the occurrence of transient phenomena and distorts the signal in the interval of the first quarter of the signal period f _m amplitude modulation. In order to prevent the distorted part of the wave from continuing beyond a quarter of the period, the carrier f _c must include at least five periods in the first quarter of the period of the amplitude modulation signal f _m . Thus, the carrier signal f _c should appear more than 20 (= 4 • 5) times in one period of the signal f _m amplitude modulation. Furthermore, it is preferable that the carrier frequency f _c be greater than the frequency of the amplitude modulation signal f _m in order to filter out the amplitude modulation signal f _m from the carrier ripple frequency f _c .

A third condition is that the continuous time of the amplitude-modulated signals preferably exceeds at least five periods of the amplitude modulation signal f _m (5 / f _m ) if the amplitude-modulated signal is demodulated to detect the amplitude modulation signal f _m . If the amplitude-modulated signal having an amplitude modulation period repeating two or three times is demodulated, then the output signal of the demodulator is distorted.

The fourth condition is that if the ultrasonic wave is cyclically propagated / received in a direction that coincides with or opposite to the flow velocity, it is desirable that the continuous time of the amplitude-modulated ultrasonic wave does not exceed half the ultrasound propagation time. You can give the following example:
5 / f _m ≤L / [2 (C + v)],
f _m ≥ [10 (C + v)] / L.

As described above, an amplitude modulation signal f _m satisfying four conditions is selected using the following expression:
f _p << 10 [(C _max + v _max ) / L] ≤f _m ≤0.05f _c , (6)
where C _max is the expected maximum speed of sound in a fluid, and V _max (= V _max cosα) is the maximum measured value of the flow velocity.

When choosing a signal f _{m of} amplitude modulation that satisfies expression (6), it is preferable to choose a relatively low frequency, since transient phenomena occur when the voltage supplied to the ultrasonic transducer changes rapidly. It is desirable that the modulation coefficient m does not exceed 50%. According to experiments, a modulation coefficient of m 25 ~ 30% is very appropriate. The attenuation coefficient of ultrasound pulsates with a lower frequency f _p , the coefficient of change of which is usually about 50%. Thus, there is a risk of cutting off the amplitude-modulated wave. For example, suppose that L = 10 m, α = 45 ^o , C _max = 1500 m / s, f _c = 500 kHz, f _p << 1507 <f _m ≤26 • 10 ³ Hz. Thus, you can select f _m in the range of 10-20 kHz. Given the transient effects of the ultrasonic wave, it is not necessary to select a higher signal frequency f _m amplitude modulation.

 FIG. 4 is a schematic block diagram illustrating a configuration of a system in accordance with one particular embodiment of the invention for implementing the flow velocity measuring method described above.

 The ultrasonic transducers 1 and 2 are connected to a switching circuit 3 of the transducers, which is switched to the state of transmission or reception. The output amplifier 18 excites the ultrasonic transducer 1 or 2. The receiving amplifier 19 amplifies the signals from the ultrasonic transducer 1 or 2, and this amplifier is a narrow-band amplifier that performs the function of automatic gain control (AGC) and amplifies only the frequency band of the amplitude modulation signal.

The amplitude modulator 17 performs amplitude modulation of the signal f _{c of the} ultrasonic carrier. The carrier generator 13 generates an ultrasonic carrier signal f _c . Generator 14 generates a modulation signal f _m of modulation smaller than the signal f _{from the} ultrasonic carrier. It should be noted here that both the carrier generator 13 and the modulation generator 14 are sine wave generators. The demodulator 20 demodulates an amplitude modulated signal to detect a frequency f _m modulation. The narrowband amplifier 21 is a narrowband amplifier that amplifies the modulation signal f _m . The zero level crossing circuit 22 produces a rectangular pulse when the first period of the output signal f _m from the narrowband amplifier 21 passes through the zero level. The device 7 for measuring the time interval measures the time interval between two pulses. The arithmetic-logic unit 8 calculates the flow velocity based on the expression for measuring the flow velocity from the difference in the propagation times of ultrasound. The switching circuit 23 allows the output signal of the frequency f _m modulation to pass through it at a predetermined time interval. The zero level crossing circuit 15 generates a rectangular pulse when the first one period the modulation signal f _m passes through the zero level. The monostable multivibrator 16 is driven by a zero level crossing circuit 15 to generate a pulse of a given duration.

 The switching circuit 24 is switched by the pulse of a monostable multivibrator 16 to provide the output signal of the modulation generator 14 to the amplitude modulator 17. The switching circuit 25 provides an ultrasonic modulated output signal to the demodulator 20, and then switches to provide input of the output signal from the receiving amplifier 19 to the amplitude modulator 20. The voltage attenuator 27 controls the output voltage of the output amplifier 18. The switching circuit controller 26 controls the switching Schemes 3, 23 and 25.

 Below, with reference to FIG. 3, a detailed explanation of the operation of the ultrasound system for measuring the speed shown in FIG. 4 is provided.

The carrier generator 13 and the modulation generator 14 are first excited to generate sine waves of frequency f _{with the} ultrasonic carrier and the modulation frequency f _m , respectively, as shown in FIGS. 3, VI and I. When the moment of measuring the flow velocity is reached, the switching circuit controller 26 supplies a rectangular a pulse of duration τ _{1 /} (see FIG. 3, II) to the switching circuit 23. The switching circuit 23 provides an input of a modulation frequency signal f _m from the modulation generator 14 to the zero level crossing circuit 15. After that, when the level of the operating potential of the zero crossing circuit 15 is set to “-” low, the zero crossing circuit 15 generates a rectangular pulse (see FIG. 3, III) when the first half-cycle of the output signal from the modulation generator 14 passes through the zero level (U = 0). This rectangular pulse is introduced into the monostable multivibrator 16, and the monostable multivibrator 16 generates a rectangular pulse of duration τ ₂ (see Fig. 3, IV). The switching circuit 24 is switched by a rectangular pulse of duration τ ₂ to provide the input of the frequency signal f _m modulation from the modulation generator 14 to the amplitude modulator 17. Thus, the frequency signal f _{c of the} ultrasonic carrier undergoes amplitude modulation for a time τ ₂ , as shown in FIG. 3 VI. Similarly, the frequency f _{c of the} ultrasonic carrier is always assumed to be amplitude modulated in the same phase of the frequency f _m modulation.

 The amplitude-modulated signal from the amplitude modulator 17 is amplified by the output amplifier 18, and then fed to the ultrasonic sensor 1. The ultrasonic sensor 1 propagates the amplitude-modulated ultrasonic wave through the fluid to the transducer 2.

At the same time, the output signal of the output amplifier 18 is inputted through the voltage attenuator 27 and the switching circuit 24 into the demodulator 20 for detecting the modulation signal f _m (Fig. 3, VII). The narrowband amplifier 21 amplifies the modulation signal demodulated by the demodulator 20 and supplies the amplified signal to the zero level crossing circuit 22. The zero level crossing circuit 22 generates a shorter rectangular pulse (FIG. 3, VIII) at the moment when the first half-period “-” of the modulation signal f _m passes through the zero level. This shorter rectangular pulse is introduced into the device 7 for measuring the time interval, performing the function of a signal to start measuring time.

 After that, the switching circuit 25 cuts off the input to the attenuator 27 and forces the output signal from the receiving amplifier 19 to the demodulator 20. In other words, the amplitude-modulated ultrasonic wave that the transducer 1 emits and propagates in the interval L is received by the transducer 2 and amplified by the receiving amplifier 19 The output signal (Fig. 3, IX) from the receiving amplifier 19 is supplied through a demodulator 20 and an amplifier 21 to the zero level crossing circuit 22. The zero level crossing circuit 22 generates a shorter rectangular pulse (FIG. 3, XI) and feeds it to the device 7 for measuring the time interval, where it performs the function of the signal of the end of the time measurement.

Then, the time interval measuring device 7 measures the time interval t ₁ between the first and second rectangular pulses from the zero level crossing circuit 22. Upon completion of the measurement of the time interval t ₁ , the converter switching circuit 3 is switched to connect the converter 2 to the output amplifier 18. Then, the switching circuit 25 is connected to the attenuator 27, and the switching circuit 23 is switched again. Subsequent operations are repeated similarly to those carried out when measuring the time interval t ₁ . Therefore, the time t ₂ is measured during the propagation period of the amplitude-modulated ultrasonic wave from the transducer 2 and its reception by the transducer 1.

The time intervals t ₁ and t ₂ are entered into the arithmetic-logical unit 8 of the flow velocity to calculate the flow velocity based on the expression (3) for measuring the flow velocity. The arithmetic-logical unit 8 of the flow rate generates a signal corresponding to the speed of the flow V. The output signal of the flow velocity V is output to the arithmetic-logical unit of the flow measurement (not shown), if the system is a system for measuring flow.

There are the following important aspects: the system has features according to which, in order to measure time intervals t ₁ and t ₂ , an amplitude-modulated output signal input to converter 1 (or 2) and a signal received by converter 2 (or 1) are passed through through one demodulator and a zero level crossing circuit, and the start and end pulses input to the device 7 for measuring the time interval are shaped like a rectangular pulse.

Expression (5), well known as an expression for measuring the flow velocity based on the phase difference, depends on the square of the speed of sound. C ² . In expression (5), Δφ is also the phase difference between ultrasonic waves propagated in directions that coincide with the flow velocity and are opposite to it. In addition to the method of measuring the flow velocity corresponding to expression (5), an expression can be derived for measuring the flow velocity based on the phase difference, which is independent of the speed of sound C.

The phase difference Δψ ₁ between the ultrasonic propagated wave and the received wave after propagation in the direction of the flow velocity and the phase difference Δψ ₂ between the ultrasonic propagated wave and the received signal after propagation in the direction opposite to the flow velocity, have the following form:
Δψ ₁ = 2πf [L / (C + v)], (7-a)
Δψ ₂ = 2πf [L / (Cv)], (7-b)
where v = Vcosα, and L is the interval between the ultrasonic transducers.

The difference between the inverse numbers of the phase differences Δψ ₁ and Δψ ₂ has the following form:
(1 / Δψ ₁ ) - (1 / Δψ ₂ ) = (2Vcosα) / (2πfL). (8)
Moreover, V has the following form:
V = [πfL / cosα] [(1 / Δψ ₁ ) - (1 / Δψ ₂ )]. (9)
This method of measuring the flow velocity is used with great benefit, since it is not necessary to measure the speed of sound separately, even if the speed of sound undergoes significant changes. But the flow velocity can be measured on the basis of expression (9) only if the error of the phase differences Δψ ₁ and Δψ _{2 is} very small - so much so that it can be ignored.

В результате,

Но фактическое значение таково:
(1/2,0)-(1/2,2)=0,0454545.For example, Δψ ₁ = 2.0 rad and Δψ ₂ = 2.2 rad. Assuming that the phase differences are measured in the error range of 0.5%, the measured phase differences have the following values:

As a result

But the actual meaning is this:
(1 / 2.0) - (1 / 2.2) = 0.0454545.

Therefore, the error has the following meaning:
(0.0406828-0.04545) / 0.04545 = -0.105 = 10.5%.

 That is, the phase differences were measured in the error range of 0.5%, but the error between the differences of the quantities inverse to the phase differences increased by more than 20 times. Thus, the error in measuring the flow velocity could become more than 10%. In order to implement a method for measuring the flow velocity based on a phase difference independent of the speed of sound C, it is necessary to measure the phase difference very accurately.

This creates the following problem arising from expression (7). With an increase in the interval L, the speed of sound C decreases, and the ultrasonic frequency increases, so that the phase difference Δψ _1,2 becomes much larger than π. Of course, if L, C, and v are given, then the ultrasonic frequency f can be chosen so that the phase difference Δψ does not exceed the measurement range π of a conventional phase difference discriminator, but this frequency should be much larger than the frequency band of the noise generated in the fluid.

For example, suppose that the internal diameter D of the pipe for natural gas is 0.3 m, C = 420 m / s, V = 30 m / s, α = 45 ^o and L = 0.425 m, then the ultrasonic frequency f, which does not exceed the phase difference π, has the following meaning:
f≤ (C + Vcosα) / 2πL = (420 + 30 • cos45 ^o ) / (2π • 0.424) = 165.6 Hz.

 A similar frequency band is included in the noise frequency band. In addition, this makes it impossible to manufacture a compact transducer that propagates a sound wave of a frequency of 165 Hz.

Отметим здесь, что 768π нельзя измерить с помощью обычного дискриминатора разности фаз.To go beyond the noise band, if the frequency f _{c is} chosen equal to 40 kHz, the phase difference in these examples should have the following values:

We note here that 768π cannot be measured using a conventional phase difference discriminator.

To solve these problems, in the invention, an ultrasonic frequency f _c extending far beyond the noise band is considered as a carrier, and its amplitude modulation is provided to a frequency f _m less than the ultrasonic frequency f _c , as well as its propagation in directions coinciding with the flow velocity and its opposite, as well as the measurement of phase differences between the propagated signal and the received signal as follows.

Firstly, a frequency f _{m of} amplitude modulation is chosen so that the phase differences Δψ _m1 and Δψ _m2 between the propagated wave of the amplitude-modulated signal and the received and demodulated signals after propagation in directions that coincide with the flow velocity and are opposite to it, satisfy the following conditions:
Δψ _m1 = 2πf _m [L / (C _max + v _max )] = nπ + bπ, (10-a)
Δψ _m2 = 2πf _m [L / (C _min -v _max )] = nπ + aπ, (10-b)
where n = const (1, 2, 3, ...), and <1.0, b <1.0, C _max and C _min are the maximum and minimum speeds of sound in a fluid, and v _max = V _max cosα - the maximum range of measurement of flow velocity.

In this case, since nπ is known in advance, it is assumed to measure the phase difference Δψ _m1 and Δψ _m2 only if aπ and bπ are measured, and then nπ is added to them. Here aπ is the maximum measurement limit, and bπ is the smallest measurement limit. Since there is instability if a = 1 and b = 0, it is desirable to choose a equal to 0.96 and choose b equal to 0.2.

 n that satisfies expression (10) is determined as follows.

The following expression for relations is defined based on expression (10):
(n + b) / (n + a) = (C _min -v _max ) / (C _max + v _max ).

где aπ = Δψ_мм1 и bπ = Δψ_мм2 представляют собой разность фаз, которую может измерить дискриминатор разности фаз. Умножая разность фаз на f_c/πf_м, получают значение, которое разделяет разности фаз Δψ_c1 и Δψ_c2 между несущими в π.

где β<1,0, γ<1,0, a m₁ и m₂ - целые числа (1, 2, 3, 4,...).Thus receive such n:
n = [a (C _min -v _max ) -b (C _max + v _max )] / ((C _max -C _min + 2v _max ). (11)
Based on n thus obtained, the modulation frequency f _m is determined as follows:
f _m = [(n + a) / 2L] (C _min -v _max ) (12-a)
or
f _m = [(n + b) / 2L] (C _max + v _max ). (12-B)
Therefore, the carrier f _{c is} subjected to amplitude modulation at a selected frequency f _m modulation, and the amplitude modulated signal is propagated / received. If the phase differences Δψ _m1 and Δψ _m2 between the modulation frequencies f _m are measured in the constant error range δ _m , the results of the calculation of the phase differences Δψ _m1 and Δψ _{m2 are} presented in the following form:

where aπ = _{Δψ mm1} and bπ = Δψ _mm2 are the phase difference that the discriminator of the phase difference can measure. Multiplying the phase difference by f _c / πf _m , we obtain a value that separates the phase differences Δψ _c1 and Δψ _c2 between the carriers in π.

where β <1.0, γ <1.0, am ₁ and m ₂ are integers (1, 2, 3, 4, ...).

Если прибавляют m₁π и m₂π к измеренным значениям, разности между фазой при распространении волны несущей и фазой принимаемого сигнала после распространения в направлениях, совпадающих со скоростью течения и противоположных ей, имеют следующий вид:

Разности фаз

полученные вышеуказанным образом, подставляются в выражения для измерения скорости течения, чтобы вычислить скорость течения следующим образом:

Если разность фаз несущих измеряют согласно вышеописанному способу, погрешность измерения уменьшается в десятки или сотни раз по сравнению с погрешностью δ_c дискриминатора разности фаз.If the phase differences Δψ _c1 and Δψ _c2 are measured as described above, then it can be seen that the values m ₁ π + βπ and m ₂ π + γπ are obtained.
The values that the discriminator measures are the following phase differences between the carriers:

If m ₁ π and m ₂ π are added to the measured values, the differences between the phase during the propagation of the carrier wave and the phase of the received signal after propagation in the directions coinciding with the flow velocity and opposite to it have the following form:

Phase differences

obtained in the above way are substituted into the expressions for measuring the flow velocity in order to calculate the flow velocity as follows:

If the phase difference of the carriers is measured according to the above method, the measurement error is reduced by tens or hundreds of times compared with the error δ _{c of the} discriminator of the phase difference.

где m₁ и m₂>>1, β и γ<1,0. Таким образом, δ_Δψc1 и δ_Δψc2 значительно меньше, чем δ_c.
Как описано выше, согласно изобретению, поскольку разность фаз точно измеряют во время распространения и приема ультразвуковой волны, можно измерять скорость течения на основании выражения для измерения скорости течения по разности фаз, которое не зависит от скорости звука. Кроме того, даже если L и V увеличиваются, а С уменьшается и разность фаз между ультразвуковыми волнами значительно превышает π радиан, можно точно измерить скорость.

where m ₁ and m ₂ >> 1, β and γ <1.0. Thus, δ _Δψc1 and δ _{Δψc2 are} much smaller than δ _c .
As described above, according to the invention, since the phase difference is accurately measured during the propagation and reception of the ultrasonic wave, it is possible to measure the flow velocity based on the expression for measuring the flow velocity by the phase difference, which is independent of the speed of sound. In addition, even if L and V increase, and C decreases and the phase difference between the ultrasonic waves significantly exceeds π radian, you can accurately measure the speed.

For example, when measuring the flow velocity of natural gas flowing in a pipe having an internal diameter of 300 mm, it is assumed that C _min = 420 m / s, C _max = 450 m / s, L = 0.425 m, V _max cosα = 30 m / s, and the frequency f _{c of the} ultrasonic carrier is chosen equal to 40 kHz, taking into account the noise in the pipe. Suppose that the measurement range of the discriminator of the phase difference is selected in the range 0 ~ π, bπ = 0.2π, for example, b = 0.2, when the phase difference becomes minimal, and aπ = 0.95π, for example, a = 0.95, when the phase difference becomes maximum in the range. Then the frequency f _m modulation will have the following meaning:
n = [0.95 (420-30) -0.2 (450 + 30)] / (450-420 + 2 • 30) = 3.05.

Under the assumption that n is chosen equal to 3 and stored in the storage device of the system, we have:
f≤ [(3.05 + 0.95) / 2 • 0.424] (420-30) = 1839.62 Hz.

Δψ_м2 = 2πf_м[L/(C-v)] = 3π+0,60893π (n = 3).
При этом известно, что разность фаз, которую может измерять дискриминатор, составляет 0,30178π или 0,60893π. В предположении, что измерение разностей фаз осуществляется с погрешностью измерения в диапазоне ±1%, вычисляемая разность фаз имеет следующее значение:

Следующая процедура такова:

Здесь нужно отметить, что m₁ (=72) сохраняется в запоминающем устройстве системы.Suppose that f _{m is} chosen equal to 1830 Hz, during the propagation of an ultrasonic wave that is amplitude-modulated at a signal level f _m amplitude modulation of 1830 Hz in directions that coincide with the flow velocity and opposite to it, and the received signal is demodulated to detect the signal f _m amplitude modulation. Then, if the phase difference between the signal phase f _{m of the} amplitude modulation of the spreading side and the phase of the received signal is measured, the results will be as follows:

Δψ _m2 = 2πf _m [L / (Cv)] = 3π + 0.60893π (n = 3).
It is known that the phase difference that the discriminator can measure is 0.30178π or 0.60893π. Under the assumption that the measurement of phase differences is carried out with a measurement error in the range of ± 1%, the calculated phase difference has the following value:

The following procedure is as follows:

It should be noted here that m ₁ (= 72) is stored in the storage device of the system.

Здесь нужно отметить, что m₂ (=78) сохраняется в запоминающем устройстве системы.

It should be noted here that m ₂ (= 78) is stored in the storage device of the system.

При этом видно, что m₁ (=72) совпало с сохраненным значением, а разность фаз Δψ_cм1 между несущими, которую можно измерить непосредственно, равна 0,17021276.The actual phase difference between the carriers has the following meaning:

It can be seen that m ₁ (= 72) coincided with the stored value, and the phase difference _{Δψ cm1} between the carriers, which can be measured directly, is 0.17021276.

При этом видно, что m₂ (=78) совпало с сохраненным значением, а разность фаз Δψ_cm2 между несущими равна 0,88372094.

It can be seen that m ₂ (= 78) coincided with the stored value, and the phase difference Δψ _cm2 between the carriers is 0.88372094.

Эти разности фаз подставляют в выражение для измерения скорости течения, вычисляя следующее значение скорости течения:

Исходная скорость Vcosα течения была равна 20 м/с, но фактически измеренная скорость течения стала равной 19,95 м/с. Таким образом, погрешность измерения составила примерно -0,15%. То есть, разности фаз были измерены два раза в диапазоне 1%. Все же, в результате этого погрешность измерения скорости течения была снижена на 0,15%.If the phase differences Δψ _c1 and Δψ _c2 are measured in the error range ± 1%, then
Δψ _cm1 = 0.54 rad
Δψ _cm2 = 2.748 rad.
The results of the calculation of the phase differences Δψ _c1 and Δψ _c2 are as follows:

These phase differences are substituted into the expression for measuring the flow velocity, calculating the following value of the flow velocity:

The initial current velocity Vcosα was 20 m / s, but the actually measured current velocity became 19.95 m / s. Thus, the measurement error was approximately -0.15%. That is, phase differences were measured twice in the range of 1%. Nevertheless, as a result of this, the error in measuring the flow velocity was reduced by 0.15%.

Разность фаз Δψ_см1 измеряли с погрешностью δ_c (=1%). Все же, погрешность Δψ_c1 измерения уменьшилась в m₁/β(=7210,1702≈423) раз (см. выражение 17). В вышеуказанном примере предполагается, что разности фаз Δψ_мм1 и Δψ_мм2 измеряют с погрешностью 1%, но на самом деле разность фаз обычно измеряют с погрешностью 0,5%.It is due to the reduction of this error are greatly reduced phase difference measurement error δψ _c1 and Δψ _c2.

The phase difference Δψ _{cm1 was} measured with an error of δ _c (= 1%). Nevertheless, the measurement error Δψ _c1 decreased by m ₁ / β (= 7210.1702≈423) times (see expression 17). In the above example, it is assumed that the phase differences _{Δψ mm1} and _{Δψ mm2} are measured with an error of 1%, but in fact the phase difference is usually measured with an error of 0.5%.

 As described above, according to the invention, the gas flow rate, when the flow velocity is large and the speed of sound is small, can be accurately measured based on the method of determining the phase difference, regardless of the change in the speed of sound in a pipe of large internal diameter.

 In FIG. 5, as one specific embodiment of the invention, a schematic block diagram is shown illustrating a system configuration for implementing a flow velocity measuring method based on a method comprising determining a phase difference.

The ultrasonic transducers 1 and 1 'are each an ultrasonic receiving transducer for receiving an ultrasonic wave, and the ultrasonic transducer 2 is
an ultrasonic propagating transducer for the propagation of ultrasonic waves with an extended directivity angle. The carrier generator 13 and the modulating wave generator 14 generate an ultrasonic carrier frequency f _c and an amplitude modulation frequency f _m , respectively. The amplitude modulator 17 performs amplitude modulation of the frequency f _{c of the} ultrasonic carrier. The output amplifier 18 drives the ultrasonic transducer 2. The receiving amplifiers 19 and 19 'amplify the signals from the ultrasonic transducers 1, 1', respectively. Demodulators 20, 20 ′ demodulate an amplitude modulated signal to detect a modulation frequency f _m . Narrow-band amplifiers 21, 21 'amplify the signals output from demodulators 20,20'. The phase difference discriminators 28, 28 ′ detect phase differences _{Δψ mm1} and _{Δψ mm2} between the amplitude modulation waves f _m . The phase difference discriminators 31 detect phase differences Δψ _cm1 and Δψ _cm2 between the carriers f _c . Limiting amplifiers 30, 30 'amplify and limit the amplitude-modulated signals to a predetermined level. The phase shifters 29, 29 'are necessary when providing forced control of the output signal of the discriminators 28, 28' of the phase difference to zero if the flow velocity V is zero. The arithmetic-logic unit 32 calculates the phase differences Δψ _c1 and Δψ _c2 between the carriers f _c , and then the flow velocity, in accordance with the invention.

 Ultrasonic system for measuring the flow velocity works as follows.

The amplitude modulator 17 performs amplitude modulation of the carrier frequency f _c generated by the carrier generator 13 into the modulation frequency f _m generated by the modulation generator 14. The amplifier 18 amplifies the amplitude-modulated signal and delivers it to the propagating ultrasound transducer 2. If the transducer 2 propagates the amplitude-modulated signal in directions that are opposite to the current velocity and opposite to it, the receiving transducer 1 receives a signal propagated in directions coinciding with the current velocity V and opposite to it, and converts it into electrical signals. The output signal from the receiving transducer 1 is amplified by the receiving amplifier 19 to amplify the frequency band f _c ± f _m and is input to the demodulator 20. An amplitude modulation signal f _{m is} generated at the output of the demodulator 20. This signal is input through a phase shifter 29 into a narrow-band amplifier 21. The narrow-band amplifier 21 again filters the amplitude-modulated signal and feeds it to the discriminator 28 of the phase difference of a lower frequency f _m . The discriminator 28 detects the signal corresponding to the phase difference Δψ _mm2 , which is less than π, and enters its output signal into the arithmetic-logical unit 32, which calculates the phase difference and the flow velocity.

An ultrasonic wave propagating in the flow velocity direction is received by the receiving transducer 1 ′, and a phase difference _{Δψ mm1 is} detected by the receiving amplifier 19 ′, a demodulator 20 ′, a narrowband amplifier 21 ′, a discriminator 28 ′, as mentioned above. At the same time, the output signal from the receiving amplifier 19 'is amplified to a saturated state by the limiting amplifier 30' and input into the discriminator 31 '. The discriminator 31 'generates signals corresponding to the phase differences Δψ _cm1 and Δψ _cm2 , and enters them into the arithmetic-logical unit 32.

It is assumed that the integers n, f _m , f _c , L, as well as an owl, are forcibly entered into the arithmetic-logical unit 32 in advance, and this unit receives m ₁ and m ₂ in accordance with expression (13), calculates the phase differences Δψ _c1 and Δψ _c2 carriers in accordance with expression (15) and calculates the flow velocity V in accordance with expression (16). The flow rate obtained in this way can be used in calculating the flow rate in case of adaptation to the flowmeter.

There is a case of measuring the speed of sound with a different method. For example, if a flowmeter for measuring a volumetric flow rate is set to measure a mass flow rate of gas, the pressure and temperature of the gas are measured separately. In this case, the speed of sound can be calculated using the results of measuring pressure and gas temperature. If fluid flow is measured in some way, there is a case where the speed of sound C in a fluid can be known in advance and does not change. In this case, ultrasonic waves propagating in directions coinciding with the flow velocity and opposite to it are received and the phase difference Δφ _c between the received signals is measured, so that the flow velocity V can be measured on the basis of expression (5). At this time, if Δφ _c >> π, Δφ _c, the phase difference is measured as follows: to carry out amplitude modulation of the ultrasound carrier frequency f _c in f _m of modulation, _m is selected modulation frequency f in the following way:
f _m ≤C ² _min / (4LV _max cosα), (18)
where C _min is the smallest expected speed of sound in a fluid.

The phase difference Δφ _m between the received signals of the amplitude-modulated frequencies thus selected does not exceed π at the maximum measured value of the flow velocity. The received amplitude-modulated signal is demodulated, so that the phase difference Δφ _m between the modulated frequencies is measured first, and then m is obtained using the following expression (19).

Δφ _m • (f _c / πf _m ) = m + a = Δφ _c / π, (19)
where a <1.0.

aπ in expression (19) is the part that can be measured in the phase difference between the carriers. At the same time, the measurement of the phase difference aπ between the carrier signals and the calculation of Δφ _{c is} carried out using the following expression.

Δφ _c = mπ + aπ. (20)
Then Δφ _{c is} substituted into expression (5) to calculate the flow velocity V. Here, the measured phase difference is aπ. When the absolute error Δaπ when measuring aπ is equal to δ _aπ • aπ (δ _aπ is the relative error), the measurement error Δφ _c has the following form:
δ _Δφc = (δ _aπ • aπ) / [(m + a) π] = δ _aπ • / (m + a).
Therefore, δ _Δφc << δ _aπ and the accuracy of calculating the flow velocity increases. Another version of the system for implementing the method of measuring the flow velocity by a similar method is depicted in the form of a conditional block diagram in Fig.6.

Turning to FIG. 6, we note that the same positions are indicated here as for identical parts in FIG. 5. It is only assumed that the integers f _m , f _c , L, as well as cosα are forced into the arithmetic-logic blocks for calculating the speed, and these blocks calculate the flow velocity based on the expressions (18), (19) and (5 )

 Therefore, the invention provides amplitude modulation of the ultrasonic wave and measurement of the flow velocity with greater reliability based on the ultrasonic method, which provides for determining the time difference in a large river, a channel of a large washing gallery, and a pipe of large internal diameter. In addition, the invention provides a method of “measuring” the flow velocity based on the phase difference, independent of the speed of sound, using a conventional phase difference discriminator having a π phase difference measurement range, even if the phase difference exceeds π radians.

Claims (4)

1. An ultrasonic method for measuring the flow velocity, comprising measuring at least two differences in the propagation times of undamped ultrasonic sinusoidal waves in opposite directions at an angle α to the direction of the flow velocity and calculating the flow velocity, characterized in that the amplitude modulation of the undamped ultrasonic sine wave carrier frequency f _{with the} signal of frequency f _m of modulation less than the carrier frequency f _c, for a period τ = 5 / f _m, carry propagation Vp bottom-modulated signals in opposite directions at an angle α to the direction of flow velocity, demodulates the received amplitude-modulated signals after spreading them in opposite directions at an angle α to the direction of flow speed, for detecting a signal frequency f _m of the amplitude modulation measured at least , two slots between the time of the amplitude modulation of the carrier frequency f of the signal _{with a} signal with frequency f _m of modulation and signal detection point f _m amplitude m of modulation of the demodulated signal after propagation of ultrasonic sine waves in opposite directions an angle α to the direction of the flow velocity and the measured time intervals t _1, t _2, calculate the flow rate from the expression
V = (L / cosα) [(1 / t ₁ ) - (1 / t ₂ )],
wherein the frequency f _{m of} the amplitude modulation signal is selected from the following expression:
f _p << 10 [(C _max + V _max cosα) / L] ≤f _m ≤0.05f _s ,
where f _p is the maximum frequency of the ripple attenuation at the time of propagation of the ultrasonic wave in the fluid;
With _max - the maximum speed of sound in a fluid medium;
L is the propagation interval of ultrasound;
V _max - the maximum expected flow rate in the interval L;
α is the angle between the direction of propagation of the ultrasonic wave and the direction of the flow velocity. 2. The ultrasonic method for measuring the flow velocity according to claim 1, characterized in that a frequency signal f _{m of} amplitude modulation, increasing from zero potential to a "+" potential, is introduced into the amplitude modulator, and then the output amplitude-modulated signal is supplied to the ultrasonic transducer and a demodulator for detecting a signal frequency f _m of amplitude modulation, determined when the amplitude-modulated signal through the first period or half period goes through zero potential level, and take his mo ent starts measuring the propagation time of ultrasound, demodulates the amplitude-modulated signal by a demodulator, wherein the amplitude-modulated signal is distributed over the interval L, and received by the other ultrasound transducer, detecting a signal frequency f _m of amplitude modulation, determined when the amplitude-modulated signal after the first period or one and a half period passes through the level of zero potential, and take it for the moment of the end of the measurement of the propagation time at trazvuka. 3. An ultrasonic method for measuring the flow velocity, including measuring the phase difference between the signals of the ultrasonic waves propagating in opposite directions at an angle α to the flow direction, and calculating the flow velocity, characterized in that the amplitude modulation of the ultrasonic wave of the carrier frequency f _{with a} signal with a frequency f _{m of} amplitude modulation less than the carrier frequency f _s , the amplitude-modulated signals propagate in opposite directions at an angle α to the direction p of the outflow, demodulate the received amplitude-modulated signals after propagating in the interval L to detect a signal of frequency f _m amplitude modulation, measure the phase difference ΔΨ _M1 between frequency signals f _m amplitude modulation, propagated and received in the direction of the flow velocity, and the phase difference ΔΨ _M2 between the signals of frequency f _m amplitude modulation, propagated and received in the opposite direction, measure at least two phase discriminators components βπ and γπ differently of the phases ΔΨ _C1 and ΔΨ _C2 between the ultrasonic signals of the carrier frequency f _c , propagated and received in the direction of the flow velocity, and between the ultrasonic signals of the carrier frequency f _c , distributed and received in the opposite direction, determine the multiples m ₁ and m _{2 of the} numbers π from the expressions
ΔΨ _C1 / π = ΔΨ _M1 (f _c / πf _m ) = m ₁ + β, (β <1,0),
ΔΨ _C2 / π = ΔΨ _M2 (f _c / πf _m ) = m ₂ + γ, (γ <1,0),
remember m ₁ and m ₂ in the storage device, calculate
ΔΨ _C1 = m ₁ π + βπ,
ΔΨ _C2 = m ₂ π + γπ,
and then calculate the current velocity V by the following expression:
V = [πf _c L / cosα] [1 / ΔΨ _C1 ) - (1 / ΔΨ _C2 )],
wherein the frequency f _m amplitude modulation is selected in accordance with the expression
f _m = [(n + a) / 2L] (C _min -V _max ),
where n = [a (C _min -V _max ) -b (C _max + V _max )] / (C _max -C _min + 2V _max ),
remember n in the storage device, measure the phase differences aπ and bπ, which can measure phase discriminators and calculate
ΔΨ _M1 = nπ + aπ,
ΔΨ _M2 = nπ + bπ,
wherein a <1.0 is the coefficient for choosing the maximum measuring range (aπ) _{max of} one of the phase discriminators, and b <1.0 is the coefficient for choosing the maximum measuring range (bπ) _{max of} another phase discriminator, C _max and C _min - maximum and minimum expected speeds of sound in a fluid, V _max - maximum expected speed of a stream. 4. An ultrasonic method for measuring the flow velocity, including measuring the phase difference Δφ _c between ultrasonic wave signals propagating in opposite directions at an angle α to the flow direction, provided that the sound velocity is measured separately or constant and the flow velocity V is calculated using the following expression:
V = (Δφ _c C ² ) / (4πfLcosα),
where C is the speed of sound;
f is the frequency of the ultrasonic wave;
L is the distance over which the ultrasonic wave propagates;
α is the angle between the direction of propagation of the ultrasonic wave and the direction of the flow velocity,
characterized in that the amplitude modulation of at least one ultrasonic wave of a carrier frequency f _{with a} signal with a frequency of f _m amplitude modulation is carried out, the amplitude-modulated signals are propagated in opposite directions, at an angle α to the flow direction, the received signals are demodulated, measured phase difference Δφ _m <π between the demodulated signals aπ measured difference in phase between the received ultrasonic signals _{with a} carrier frequency f by the phase discriminator, GER Delyan multiple m and the number of expressions
Δφ _m • (f _c / πf _m ) = m + a = Δφ _c / π (a <1,0),
and calculate Δφ _c = mπ + aπ, and then calculate the flow velocity V by the phase difference Δφ _c , while the frequency f _m amplitude modulation is selected from the expression
f _m ≤C $\genfrac{}{}{0ex}{}{\text{2}}{\text{min}}$ / (4LV _max cosα),
where C _min is the smallest expected speed of sound in a fluid;
V _max - the maximum expected flow rate in the interval L.

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