CN113375737B - Flow velocity metering method of time difference type ultrasonic gas flowmeter - Google Patents
Flow velocity metering method of time difference type ultrasonic gas flowmeter Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
- G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
- G01F1/668—Compensating or correcting for variations in velocity of sound
Abstract
Embodiments of the present disclosure disclose a flow rate metering method of a transit time ultrasonic gas flow meter. One embodiment of the method comprises the following steps: acquiring attitude information of an upstream ultrasonic transducer and a downstream ultrasonic transducer; acquiring the propagation distance of an ultrasonic signal from an upstream ultrasonic transducer to a downstream ultrasonic transducer; determining a time difference by the cross-power spectral density function and the coherence function, wherein the time difference is the difference between the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal; analyzing the upstream ultrasonic signal and the downstream ultrasonic signal based on Hilbert transform, and determining a variable threshold; determining a transit time of the upstream ultrasonic signal and a transit time of the downstream ultrasonic signal based on the variable threshold; and determining the flow velocity of the medium detected by the flowmeter according to the propagation distance, the attitude information, the time difference, the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal. This embodiment enables an accurate calculation of the medium flow rate.
Description
Technical Field
The embodiment of the disclosure relates to the field of flowmeters, in particular to a flow rate metering method of a time difference type ultrasonic gas flowmeter.
Background
Ultrasonic gas flow meters have been increasingly used in numerous fields of industry and life. For example, ultrasonic gas flow meters can measure the flow of natural gas, chlorine in water treatment, and multi-component gases.
The existing ultrasonic gas flowmeter is often calculated by adopting a time difference method. As an example, a dual threshold comparison method is typically employed to determine the flow measurement of a time-difference ultrasonic flow meter, with the emphasis on calculating the exact time of the signal to the over-threshold point. However, the above methods are susceptible to noise interference. When the starting point amplitude of the echo signal is low or two very close maximum points, it is difficult to identify. Thereby affecting the accuracy of the measured values.
As another example, the method of determining the position of the echo signal by setting the transformation ratio threshold value and finding the feature point is also used, so as to calculate the threshold scaling factor according to the peak value of the echo signal and the peak value of the corresponding echo signal. However, when the flow velocity changes rapidly, the change speed of the echo energy integration is easily disturbed by noise in the gas, so that instability exists in the change of the characteristic point, and the accuracy of the measured value is further affected.
As yet another example, the transit time of the ultrasonic signal can also be calculated by using a cross-correlation method in the time domain, which can solve the two problems described above. However, the cross-correlation method requires interpolation to improve accuracy, searches for an appropriate reference signal, and has a large calculation amount.
Accordingly, there is a need in the art for a new method of determining the flow rate of a jet lag ultrasonic gas flow meter.
Disclosure of Invention
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
Some embodiments of the present disclosure propose a flow rate metering method, apparatus, electronic device and computer readable medium for a time-lapse ultrasonic gas flow meter to solve the technical problems mentioned in the background section above.
Some embodiments of the present disclosure provide a flow rate metering method of a time-lapse ultrasonic gas flow meter, the method comprising: acquiring attitude information of an upstream ultrasonic transducer and a downstream ultrasonic transducer; acquiring the propagation distance of an ultrasonic signal from an upstream ultrasonic transducer to a downstream ultrasonic transducer; determining a time difference by a cross-power spectral density function and a coherence function, wherein the time difference is the difference between the transit time of an upstream ultrasonic signal and the transit time of a downstream ultrasonic signal; analyzing the upstream ultrasonic signal and the downstream ultrasonic signal based on a hilbert transform to determine a variable threshold; determining a transit time of the upstream ultrasonic signal and a transit time of the downstream ultrasonic signal based on the variable threshold; and determining the flow rate of the medium detected by the flowmeter according to the propagation distance, the attitude information, the time difference, the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal.
In some embodiments, the above flow rate is determined by the following formula: wherein v represents the flow rate of the medium detected by the flowmeter; l represents the propagation distance; θ represents the included angle between the upstream ultrasonic transducer and the downstream ultrasonic transducer and the pipe wall of the medium; Δt represents a time difference; t (T) u Representing a transit time of the upstream ultrasonic signal; t (T) d Representing the transit time of the downstream ultrasonic signal.
In some embodiments, determining the time difference from the cross-power spectral density function and the coherence function includes: acquiring an upstream echo signal and a downstream echo signal; determining the correlation degree of the upstream echo signal and the downstream echo signal in the time domain through a cross-correlation function; the cross-correlation function of the upstream echo signal and the downstream echo signal in the time domain is:
wherein t represents a selected time; τ represents a time delay between the upstream echo signal and the downstream echo signal; representing the degree of correlation between the upstream echo signal and the downstream echo signal at a time delay τ; x (t) represents the amplitude of the upstream echo signal or the downstream echo signal at time t; y (t+τ) represents the amplitude of the downstream echo signal or the upstream echo signal at time t+τ; t represents the period of sampling; for discrete time, the above correlation function is converted into:
wherein m represents a selected discrete time; n represents a discrete time delay between the downstream echo signal and the upstream echo signal; n represents the period of discrete samples.
In some embodiments, determining the time difference from the cross-power spectral density function and the coherence function includes: the cross power spectral density function of the upstream echo signal and the downstream echo signal is:wherein e -j2πωτ Representing a complex function; the cross-power spectral density function is expressed in complex form, with complex polar coordinates as follows:
wherein Im [ P ] xy (ω)]An imaginary numerical component representing a cross-power spectral density function; re [ P ] xy (ω)]A real number component representing a cross-power spectral density function; j represents an imaginary number; the correlation between the upstream echo signal and the downstream echo signal in the frequency domain is determined by the following formula:
wherein, gamma 2 xy (ω) is the amplitude squared coherence as a function of the power spectral density, representing the correlation of the upstream echo signal and the downstream echo signal in the frequency domain, also called correlation coefficient, with a maximum of 1; p (P) x (ω) represents a self-power spectral density function of x; p (P) y (ω) represents a self-power spectral density function of y; wherein w is m Indicating whenWhen the value is maximum, the value of w is taken; omega m Also indicates the signal frequency, at which time the phase difference between the upstream echo signal and the downstream echo signal is θ xy (w m ) According to the relationship between the cross power spectrum phase and the frequency, the phase difference can be obtained by a trigonometric function relationship;the above time difference is determined according to the following formula: />
In some embodiments, determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises: the variable threshold is determined by the following formula: δ=0.1 max (a (t)); wherein δ represents a variable threshold; a (t) represents an envelope of the upstream echo signal or the downstream echo signal; wherein, the A (t) is determined by the following formula:wherein x (t) represents an upstream or downstream signal: the above X (t) is determined by the following formula:
wherein (1)>The convolution of x (t) and 1/pi t is represented by the formula:wherein H [ x (t)]The Hilbert transform of x (t) is represented.
In some embodiments, determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises: determining a maximum value of the upstream echo signal or the downstream echo signal envelope curve rising stage; the local maximum point is determined by the following formula: nn (nn) 0 =o+δ; wherein nn 0 Representing local maximum point Z 0 Is the ordinate of (2); delta represents a variable threshold; o represents the minimum difference between the variable threshold and the local maximum ordinate; wherein, O is determined by the following formula: o=min (|δ -nn) i I), where nn i Representing the i-th local maximum Z i Is the ordinate of (2); by applying to said local maximum point Z 0 Two adjacent sampling points S -1 ，S +1 Performing parabolic interpolation processing on the three points to obtain a peak value; determining the peak value as an upstream feature point or a downstream feature point S p (m p ,n p ) The method comprises the steps of carrying out a first treatment on the surface of the The transit time of the upstream echo signal or the downstream echo signal is determined according to the following formula: t (T) u ＝T p +T u ’；T d ＝T p +T d 'A'; wherein T is P Representing a fixed time from the sending of the upstream ultrasonic signal or the downstream ultrasonic signal to the receiving of the upstream echo signal or the downstream echo signal, which is obtained according to experiments; t (T) u ' represents the time from the start of sampling of the upstream echo signal to the upstream feature point; t (T) d ' represents the time from the start of sampling of the downstream echo signal to the downstream feature point; wherein T is as described above d ' is determined by the following formula: t (T) d ’＝m p1 Fs; wherein m is p1 Representing downstream feature points S p1 Is the abscissa of (2); fs represents the sampling rate; wherein, tu' is determined by the following formula: tu' =m p2 /Fs, where m p2 Representing upstream feature points S p2 Is defined by the abscissa of the (c).
One of the above embodiments of the present disclosure has the following advantageous effects: firstly, the time delay is directly calculated by adopting a cross power spectrum method, the time difference of the upstream and downstream flight signals is determined, and compared with the related algorithm for respectively calculating the time of the upstream and downstream flight signals, the calculated amount is reduced. Meanwhile, the mutual power method is an unsteady process, and can directly obtain nanosecond accurate time delay. And further improves the accuracy of flow rate calculation.
In addition, the Hilbert transform is adopted to determine the variable threshold, different thresholds are set according to waveforms of different signals, and then the position of the echo signal is determined more accurately. Thereby improving the accuracy of the method.
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The above and other features, advantages, and aspects of embodiments of the present disclosure will become more apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings. The same or similar reference numbers will be used throughout the drawings to refer to the same or like elements. It should be understood that the figures are schematic and that elements and components are not necessarily drawn to scale.
FIG. 1 is a schematic diagram of a reflection type structure of a jet lag ultrasonic gas flow meter according to some embodiments of the present disclosure;
FIG. 2 is a flow chart of some embodiments of a flow rate metering method of a jet lag ultrasonic gas flow meter according to some embodiments of the present disclosure;
FIG. 3 is a schematic diagram of upstream and downstream ultrasonic transmit signals and upstream and downstream echo signals of the present disclosure;
FIGS. 4 and 5 are cross-power spectral phase diagrams of an upstream echo signal and a downstream echo signal, respectively;
FIGS. 6 and 7 are graphs showing the degree of correlation of the upstream echo signal and the downstream echo signal, respectively;
FIG. 8 is a schematic diagram of a first echo signal or a second echo signal;
FIG. 9 is a schematic diagram of a functional block diagram of portions of the ultrasonic flow meter;
FIG. 10 is a transition time T of an upstream echo signal u Transit time T of downstream signal d And a data table of the relationship of the time difference Δt at 9 flow points;
FIG. 11 is a schematic diagram of an approximate linear relationship of time-of-flight differences to standard flow points;
FIG. 12 is a schematic illustration of an ultrasonic flow meter calibration test;
fig. 13 and 14 are schematic diagrams of the results of performing a zero drift experiment at high temperatures of 25.9 ℃ and 70.0 ℃ at an order of 30 for the filter of the moving average;
FIG. 15 is a schematic diagram of errors in K-value verification of 9 dynamic flow points based on the method described above;
FIG. 16 shows the repeatable error results for dynamic flow points;
FIG. 17 shows a schematic diagram of an indication error of measurement results of the present disclosure;
fig. 18 is a schematic diagram of repeatability of the measurement results of the present disclosure and of conventional measurement results.
Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. It should be understood that the drawings and embodiments of the present disclosure are for illustration purposes only and are not intended to limit the scope of the present disclosure.
It should be noted that, for convenience of description, only the portions related to the present invention are shown in the drawings. Embodiments of the present disclosure and features of embodiments may be combined with each other without conflict.
It should be noted that the terms "first," "second," and the like in this disclosure are merely used to distinguish between different devices, modules, or units and are not used to define an order or interdependence of functions performed by the devices, modules, or units.
It should be noted that references to "one", "a plurality" and "a plurality" in this disclosure are intended to be illustrative rather than limiting, and those of ordinary skill in the art will appreciate that "one or more" is intended to be understood as "one or more" unless the context clearly indicates otherwise.
The names of messages or information interacted between the various devices in the embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of such messages or information.
The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Referring first to fig. 1, fig. 1 is a schematic diagram of a reflection type structure of a transit time ultrasonic gas flow meter according to some embodiments of the present disclosure. As shown in fig. 1, an ultrasonic gas flow meter generally includes an upstream ultrasonic transducer 1, a downstream ultrasonic transducer 2. The upstream ultrasonic transducer 1 and the downstream ultrasonic transducer 2 are symmetrically inserted into the pipeline 3. In the working state, the upstream ultrasonic transducer 1 sends out an upstream ultrasonic signal, and the upstream ultrasonic signal is reflected by the inner wall of the pipeline 3 and received by the downstream ultrasonic transducer 2. The time from the upstream ultrasonic signal to the downstream ultrasonic transducer 2 may be referred to as the transit time T of the downstream ultrasonic signal d . Meanwhile, the downstream ultrasonic transducer 2 emits a downstream ultrasonic signal, which is reflected by the inner wall of the pipe 3 and received by the upstream ultrasonic transducer 1. The time from the downstream ultrasonic transducer 2 to the upstream ultrasonic transducer 1 of the downstream ultrasonic signal may be referred to as the upstream ultrasonic signal transit time T u . The propagation distance L of the upstream ultrasonic signal can be determined by the pipeline diameter D and the placement posture of the upstream ultrasonic transducer or the downstream ultrasonic transducer. The above-mentioned placement posture can be the included angle θ of the upstream ultrasonic transducer or the downstream ultrasonic transducer with the pipe wall of the carried medium. Next, the flow rate of the medium in the conduit may be determined by the following formula:
wherein DeltaT represents the upstream ultrasonic signal transit time T u And the transit time T of the downstream ultrasonic signal d Is a time difference of (2).
Referring next to fig. 2, fig. 2 is a flow 200 of some embodiments of a flow rate metering method of a transit time ultrasonic gas flow meter according to some embodiments of the present disclosure. The method comprises the following steps:
and step 201, acquiring attitude information of the upstream ultrasonic transducer and the downstream ultrasonic transducer.
In some embodiments, the gesture information may be an angle of the upstream ultrasonic transducer and the downstream ultrasonic transducer with respect to the pipeline when the upstream ultrasonic transducer and the downstream ultrasonic transducer are inserted into the pipeline. Typically the upstream ultrasonic transducer and the downstream ultrasonic transducer are arranged in a symmetrical manner into the pipeline. The execution body may be a data processing module of the flowmeter. The staff can input the included angle data into the data processing module through the man-machine interaction interface between the upstream ultrasonic transducer and the included angle between the downstream ultrasonic transducer and the pipeline.
Step 202, a propagation distance of an ultrasonic signal from an upstream ultrasonic transducer to a downstream ultrasonic transducer is obtained.
In some embodiments, the propagation distance may be calculated from the inner diameter of the pipeline and the angle data obtained in step 202. Likewise, the inner diameter of the pipeline can be input into the execution body through a man-machine interaction interface. Specifically, the description is given with reference to fig. 1. The propagation distance L may be twice the quotient of the in-line channel D and sin θ. I.e.
In step 203, a time difference is determined from the cross-power spectral density function and the coherence function.
In some embodiments, the time difference represents the upstream ultrasonic signal transit time T u And the transit time T of the downstream ultrasonic signal d Is a time difference of (2).
Referring specifically to fig. 3, fig. 3 is a schematic diagram of upstream and downstream ultrasonic signals and upstream and downstream echo signals of the present disclosure. The time difference may be determined by:
in a first step, an upstream echo signal 12 and a downstream echo signal 22 are acquired. Specifically, the upstream echo signal 12 and the downstream echo signal 22 may be acquired by a downstream ultrasonic transducer or an upstream ultrasonic transducer. Those skilled in the art can preprocess the upstream echo signal 12 and the downstream echo signal 22, and then acquire the upstream echo signal 12 or the downstream echo signal 22 through the downstream ultrasonic transducer or the receiving array element of the upstream ultrasonic transducer.
And a second step of determining the correlation degree of the upstream echo signal and the downstream echo signal in the time domain through a cross-correlation function. The cross-correlation degree is determined by a cross-correlation function, and the specific formula is as follows:wherein t represents a selected time, wherein the selected time may be set by a technician or set by the execution subject by default; τ represents the time delay of the upstream echo signal and the downstream echo signal, and is also the abscissa of the cross-correlation function, the value range is between 0 and T, and τ can be selected by a technician or by default setting of an execution main body; representing the degree of correlation of the upstream echo signal and the downstream echo signal at a time delay tau; x (t) represents the amplitude of the upstream echo signal or the downstream echo signal at time t; y (t+τ) represents the amplitude of the downstream echo signal or the upstream echo signal at time t+τ; t represents a sampling period, which may be set by a technician or may be set by the execution body by default, for example; for discrete time, the above correlation function is converted into: />Wherein m represents a selected discrete time, wherein the discrete time can be set by a technician or can be set by the execution main body in a default manner; n represents the discrete time delay of the downstream echo signal and the upstream echo signal, and is also the abscissa of the discrete cross-correlation function, the value range is an integer between 0 and N, NThe selection of (2) can be selected by a technician or can be set by a default of an execution main body; n represents a period of discrete sampling, which may be set by a technician or may be set by the execution body by default.
Next, a cross-power spectral density function of the upstream echo signal and the downstream echo signal is:wherein e -j2πωτ Representing a complex function; the cross-power spectral density function is expressed in complex form, with complex polar coordinates as follows: /> Wherein P is xy (ω) represents a cross-power spectral density function; im [ P ] xy (ω)]An imaginary numerical component representing a cross-power spectral density function; re [ P ] xy (ω)]A real number component representing a cross-power spectral density function; j represents an imaginary number. Reference may be made to fig. 4 and 5, fig. 4 and 5 being inter-spectral phase diagrams of an upstream echo signal and a downstream echo signal, respectively. The correlation between the upstream echo signal and the downstream echo signal in the frequency domain is determined by the following formula: />Wherein, gamma 2 xy (ω) is an amplitude squared coherence function representing the correlation of the upstream echo signal and the downstream echo signal in the frequency domain, also called correlation coefficient, with a maximum of 1; p (P) x (ω) represents a self-power spectral density function of x, where x represents an upstream echo signal; p (P) y (ω) represents a self-power spectral density function of y, where y represents the downstream echo signal. Wherein w is m Indicating when->When the value is maximum, the value of w is taken; omega m Also watchShowing the signal frequency. Reference may be made to fig. 6 and 7, and fig. 6 and 7 are schematic diagrams of the degree of correlation of the upstream echo signal and the downstream echo signal, respectively. At this time, the phase difference between the upstream echo signal and the downstream echo signal is θ xy (w m ) The method comprises the steps of carrying out a first treatment on the surface of the According to the relationship between the cross-power spectrum phase and frequency, the phase difference can be obtained by a trigonometric function relationship: />The above time difference is determined according to the following formula: />
In some embodiments, determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises:
the variable threshold is determined by the following formula:
δ=0.1 max (a (t)); wherein δ represents a variable threshold; a (t) represents an envelope of the upstream echo signal or the downstream echo signal; wherein, the A (t) is determined by the following formula:where x (t) represents an upstream echo signal or a downstream echo signal: wherein, the->Is determined by the following formula:wherein (1)>The convolution of x (t) and 1/pi t is represented by the formula:wherein H [ x (t)]The Hilbert transform of x (t) is represented.
In some embodiments, determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises:
and determining a maximum value of which the slope is positive and the amplitude is greater than 0 in the upstream echo signal or the downstream echo signal envelope curve rising stage. Specifically, the description is given with reference to fig. 8. Fig. 8 is a schematic diagram of a first echo signal or a second echo signal. As shown in fig. 8, the local maxima are the numerical values of the positions characterized by the "triangle" in fig. 8; the local maximum point is determined by the following formula: nn (nn) 0 =o+δ; wherein nn 0 Representing local maximum point Z 0 Is the ordinate of (2); delta represents a variable threshold; o represents the minimum difference between the variable threshold and the local maximum; wherein, the above O is determined by the following formula: o=min (|δ -nn) i |) is provided; wherein nn i Representing the i-th local maximum Z i Is the ordinate of (2); by applying to the local maximum point Z 0 Two adjacent sampling points S -1 ，S +1 Performing parabolic interpolation processing on the three points to obtain a peak value; determining the peak value as an upstream feature point or a downstream feature point S p (m p ,n p )。
Next, determination of the transit time of the upstream echo signal or the downstream echo signal will be described with reference to fig. 8. Specifically, the transit time of the upstream echo signal or the downstream echo signal may be determined according to the following formula: t (T) u ＝T p +T u ’；T d ＝T p +T d 'A'; wherein T is P The fixed time obtained by experiments from the time when the upstream ultrasonic signal or the downstream ultrasonic signal is sent to the time when the upstream echo signal or the downstream echo signal is received is represented, and the fixed time can be adjusted according to the pipeline size. T (T) u ' represents the time from the start of sampling of the upstream echo signal to the upstream feature point; t (T) d ' represents the time from the start of sampling of the downstream echo signal to the downstream feature point, wherein T is d ' is determined by the following formula: t (T) d ’＝m p1 Fs; wherein m is p1 Expressed belowThe tour feature point S p1 Is the abscissa of (2); fs represents the sampling rate, wherein, T is u ' is determined by the following formula: t (T) u ’＝m p2 /Fs, where m p2 Representing upstream feature points S p2 Is defined by the abscissa of the (c).
According to the flow velocity metering method of the time difference type ultrasonic gas flowmeter, firstly, the time delay is directly calculated by adopting a cross power spectrum method, the time difference of the upstream and downstream flight signals is determined, and compared with a related algorithm for respectively calculating the time of the upstream and downstream flight signals, the flow velocity metering method reduces the calculated amount. Meanwhile, the mutual power method is an unsteady process, and can directly obtain nanosecond accurate time delay. And further improves the accuracy of flow rate calculation.
In addition, the Hilbert transform is adopted to determine the variable threshold, different thresholds are set according to waveforms of different signals, and then the position of the echo signal is determined more accurately. Thereby improving the accuracy of the method.
The following is a calibration experiment performed.
First, a calibration device is described. The calibration device is a sonic nozzle calibration device, and the uncertainty of the calibration device is 0.5%. When the test meter is calibrated, the test meter is mounted on the pipeline. The sonic nozzle type calibration device provides standard flow for the test instrument. The test instrument measures the pulse rate according to the magnitude of the pulse coefficient and converts the frequency value into the pulse number. The pulse equivalent K of the test meter was set to 500 pulses/m 3 .500 pulses represent 1m 3 /h。
Specifically, the ultrasonic flowmeter will be described with reference to fig. 9. Fig. 9 is a schematic diagram of a functional block diagram of the various parts of the ultrasonic flowmeter. As shown in fig. 9, the apparatus includes a flow meter prototype, an ultrasonic sensor, a pulse emission driving module, an amplifier filtering module, a comparator module, a timing module, a power module, a control data processing module, and a memory display module. The ultrasonic transducer can send an excitation signal and receive an echo signal, and the center frequency of the ultrasonic transducer is 200KHz. JK transducer mounted in very small diameter (176.7 mm) 2 ) Experimental data acquisition is performed, and the feasibility of the algorithm is verifiedSex. And in medium-sized pipes (1963.5 mm) 2 ) Experimental verification was performed above. It has good portability.
In the formula Is constant (I)>The value of (2) determines the final average flow, and experiments show that the delta T time difference plays a decisive role in the calculation.
Deltat is a numerator that is about 1 to 400 times the dynamic range of the denominator. The denominator is the product of the transit time of the upstream echo signal and the transit time of the downstream echo signal, and the relative molecular variation is not large within the complete denominator range. The abrupt change in the time difference reflects the abrupt change in the flow rate. The importance of the time difference is further verified and can be explained in connection with fig. 10. FIG. 10 is a transition time T of an upstream echo signal u Transit time T of downstream signal d And a data table of the relationship of the time difference Δt at 9 flow points. The graph shows that the cross-sectional area S is 176.7mm 2 At 100T d ，T u And the average value of Δt. At the same time, the effect of temperature on this conclusion is also discussed. When the temperature is raised to 70 ℃, T u And T d Will decrease somewhat at the same time, however, T d ×T u The contribution of the values of (c) to the overall flow calculation is also much smaller than deltat.
Next, the importance of the accuracy Δt can be seen from the relationship between the calculation data Δt and the average flow velocity v as well, and the measurement result of Δt can be seen from fig. 10. Fig. 11 is a schematic diagram of the approximate linear relationship of the moveout parameter to the standard flow point, thereby verifying the meaning of precisely calculating the moveout. There are 100 sets of time reference values at 9 standard flow points in the graph, and the concentration degree of time delay at each standard flow point is given.
Specifically, the experimental results are divided into two parts, one being a static result and the other being a dynamic indication error and repeatability result at 9 standard flow points. Static experiments were performed at normal temperature (25.9 ℃) and high temperature (70.0 ℃). The static condition is that the pipeline is spirally connected by the rubber cover, so that the static condition is ensured.
At this time, the zero point of the ultrasonic gas flow meter is detected at a static flow rate. The propagation time of the ultrasonic wave can be calculated according to the ultrasonic sound velocity, the ultrasonic sound velocity at the ambient temperature and the length of the ultrasonic propagation channel. By this method and experiment we can roughly estimate the propagation time T of the pulse p For determining a fixed value between an ADC (Analog-to-Digital Converter) acquisition window and pulse emission. Then, according to the accumulated flow rate in a period of time, obtaining 0m 3 The average measurement error of/h, and record K in software, finish zero calibration. The experimental measurements were performed on a sonic nozzle gas meter calibration apparatus, as shown in fig. 12. Fig. 12 is a schematic diagram of an ultrasonic flow meter calibration test. The proposed ultrasonic flow meter system has been designed for use with reflective structure flow meters. The algorithm has been tested in 2 pairs of 500kHz transducers and 5 pairs of 200kHz transducers.
Referring next to fig. 13 and 14, fig. 13 and 14 are schematic illustrations of near zero measurements at high temperatures of 25.9 ℃ and 70.0 ℃ respectively, with a moving average filter order of 30.
The unfiltered and filtered maximum zero drift flows at 25.9 ℃ were respectively: q= 0.01567m 3 H and q= 0.00272m 3 And/h. At a high temperature of 70.0 ℃, the unfiltered and filtered maximum zero drift flows are q= 0.01935m respectively 3 H and q= 0.00295m 3 And/h. The original measured flow rates measured in fig. 13 and 14 are broken line portions in the graph, the broken line portions representing the start-up flow rates, and the curve portions representing the flow rates after filtering. And adds a visual comparison. As can be seen from fig. 13 and 14, the flow calculation model composed of the analysis model and the averaging method satisfies the zero point error requirement.
Before the zero point test experiment starts, the experiment sample is takenThe instrument of the machine was placed in a high and low temperature laboratory box and the temperature was gradually increased to 70 ℃ over 2 hours. This temperature was maintained for 2 hours. During this period, the air temperature was stabilized at 70℃and the fluctuation was 1%. Zero drift is achieved at high temperatures. At the zero flow point, the calculated flow requirement is smaller than the initial flow q according to the national standard s At this time, no stream is defaulted. The pickup flow rate of the G4 table was 0.003m 3 And/h. FIG. 15 is a test result at a high temperature of 70 ℃. From the experimental results, it can be seen that the zero flow drift problem can be satisfied even at a high temperature of 70 ℃.
For the dynamic results, an aerodynamic experiment was performed on a standard sonic nozzle gas meter calibration device and the measurement performance of the prototype gas flow meter was tested. The center frequency and diameter of the cylindrical transducer were 200kHz and 18mm, respectively. The AD sampling rate was 1MHz. The system is suitable for accurate gas metering at very small flow rates. The flow velocity detection range is 0.04-6.00 m 3 And/h. The volume of the reference gas was measured by a sonic nozzle type calibration device, and the uncertainty was 0.5%, and the temperature was about 25℃at room temperature. Three equivalent limits (minimum gas power qmin, transition gas power, maximum gas power q) should be determined within the measured power range according to the specification of the "ultrasonic gas flow meter calibration protocol max ) Q herein t ＝0.1q max . Thus, the gas flow rate is set to be in the range of 0.04-6.00 m 3 Per h) at 0.6m 3 The demarcation flow rate/h is divided into two groups, and the requirements on the indication error and the repeatability are different in the two flow rate ranges.
The final flow value needs to be checked with a K value. The flow calculation formula is as follows: q= KvS, where S is the cross-sectional area of the duct, and different flow points have different K values. Fig. 15 is a schematic diagram of indication errors of K-value verification for 9 dynamic flow points based on the above method. Since the K-value verification can correct the indication error correctly, the key role of repeatability is illustrated. The calculation of the transit time of the echo signal uses the Hilbert transform to set a variable threshold. The comparison of the conventional measurement method with the measurement method of the present disclosure at 9 dynamic flow points is shown in fig. 16. Fig. 16 shows the repeatable error results for the dynamic flow point.
Fig. 15 and 16 show the recognition error and repeatability under the condition of extremely small pore diameter for k-value verification, respectively, and the results of calculation of the two principles are compared. As described in connection with fig. 17, fig. 17 shows the indication error of the measurement result of the present disclosure, in the case of a small flow rate, the repeatability of the conventional measurement method is difficult to ensure and the proposed method satisfies the accuracy requirement. In modern ultrasonic flow measurement, accurate measurement of high-precision small flow is a key for realizing an overall high-precision dynamic measurement result.
Fig. 18 is a schematic diagram illustrating the repeatability of the measurement results of the present disclosure and the conventional measurement results, described in connection with fig. 18. The experimental subject was a very small diameter flow meter with a cross-sectional diameter of 176.7mm 2 . It has high requirement for repeatability at small flow rates. In this case, it is necessary to measure the time difference more accurately. This method recalculates a time difference rather than directly subtracting the absolute time of flight.
The flow velocity metering method of the time difference type ultrasonic gas flowmeter, disclosed by the invention, utilizes the approximate linear relation between the time difference and the standard flow to verify the importance of the time difference in flow calculation. The effect of dynamic changes in the time difference values on the flow calculation of the full time difference formula is analyzed. This makes accurate measurement of the transit ultrasonic gas flow meter critical to time difference estimation. A separation model of the time difference from the upstream and downstream echo signals is established. And the cross power spectrum method is used for calculating the phase difference analysis of the uplink and downlink signals to obtain a time difference, and the Hilbert transform is used for setting a variable threshold value to obtain absolute flight absolute time, so that the calculated amount is reduced. After K value inspection, the error of the indication value is reduced, and the repeatability is the most important index of the whole ultrasonic measurement system. The above experiments compare the calculated time delay subtracted by the variable thresholding method with the repeatability of the proposed method. Experimental results show the superiority of the algorithm and the superiority of the model.
The algorithm has higher precision, and experimental results also prove that the algorithm is suitable for small pipelines capable of accurately detecting flow. Under the condition of large flow, the methodThe results of (2) are also stable, meeting the repeatability requirements. The algorithm has been transplanted to a pipeline with a cross-sectional area of 1963mm 2 Good reproducibility results were obtained.
The foregoing description is only of the preferred embodiments of the present disclosure and description of the principles of the technology being employed. It will be appreciated by those skilled in the art that the scope of the invention in the embodiments of the present disclosure is not limited to the specific combination of the above technical features, but encompasses other technical features formed by any combination of the above technical features or their equivalents without departing from the spirit of the invention. Such as the above-described features, are mutually substituted with (but not limited to) the features having similar functions disclosed in the embodiments of the present disclosure.
Claims (1)
1. A flow rate metering method of a time difference type ultrasonic gas flowmeter, wherein the time difference type ultrasonic gas flowmeter is a flowmeter with a small diameter, and the diameter of the cross section is 176.7mm 2 The flow rate range is 0.04-6.00 m 3 /h, comprising:
acquiring attitude information of an upstream ultrasonic transducer and a downstream ultrasonic transducer, wherein the attitude information is an included angle relative to a pipeline when the upstream ultrasonic transducer and the downstream ultrasonic transducer are inserted into the pipeline;
acquiring the propagation distance of an ultrasonic signal from the upstream ultrasonic transducer to the downstream ultrasonic transducer;
determining a time difference by a cross-power spectral density function and a coherence function, wherein the time difference is the difference between the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal;
analyzing the upstream ultrasonic signal and the downstream ultrasonic signal based on a Hilbert transform to determine a variable threshold;
determining a transit time of the upstream ultrasonic signal and a transit time of the downstream ultrasonic signal based on the variable threshold;
determining a flow rate of the medium detected by the flowmeter according to the propagation distance, the attitude information, the time difference, the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal;
wherein the flow rate is determined by the following formula:
wherein v represents the flow rate of the medium detected by the flowmeter;
l represents the propagation distance;
θ represents the angles between the upstream ultrasonic transducer and the downstream ultrasonic transducer and the wall of the medium;
DeltaT represents the time difference;
T u representing a transit time of the upstream ultrasonic signal;
T d representing a transit time of the downstream ultrasonic signal;
wherein said determining a time difference by a cross-power spectral density function and a coherence function comprises:
acquiring an upstream echo signal and a downstream echo signal;
determining the correlation degree of the upstream echo signal and the downstream echo signal in the time domain through a cross-correlation function;
the cross-correlation function of the upstream echo signal and the downstream echo signal in the time domain is:
wherein t represents a selected time;
τ represents a time delay of the upstream echo signal and the downstream echo signal;
R xy (τ) represents a degree of correlation of the upstream echo signal and the downstream echo signal at a time delay τ;
x (t) represents the amplitude of the upstream echo signal or the downstream echo signal at time t;
y (t+τ) represents the amplitude of the downstream echo signal or the upstream echo signal at time t+τ;
t represents the period of sampling;
for discrete time, the correlation function is converted into:
wherein m represents a selected discrete time;
n represents a discrete time delay of the downstream echo signal and the upstream echo signal;
n represents the period of discrete samples;
wherein said determining a time difference by a cross-power spectral density function and a coherence function comprises:
the cross power spectral density function of the upstream echo signal and the downstream echo signal is:
wherein e -j2πωτ Representing a complex function;
the cross-power spectral density function is expressed in complex form, and the complex polar form is as follows:
wherein Im [ P ] xy (ω)]An imaginary numerical component representing a cross-power spectral density function;
Re[P xy (ω)]a real number component representing a cross-power spectral density function;
j represents an imaginary number;
the correlation of the upstream echo signal and the downstream echo signal in the frequency domain is determined by the following formula:
wherein, gamma 2 xy (ω) is the amplitude squared coherence as a function of the power spectral density, representing the correlation of the upstream echo signal and the downstream echo signal in the frequency domain, also called correlation coefficient, with a maximum of 1;
P x (ω) represents a self-power spectral density function of x;
P y (ω) represents a self-power spectral density function of y;
wherein omega m Indicating whenWhen the value is maximum, the value of omega is taken; omega m Indicating the signal frequency, the phase difference between the upstream echo signal and the downstream echo signal is theta xy (ω m ) According to the relationship between the cross-power spectrum phase and the frequency, the phase difference can be obtained by a trigonometric function relationship:
the time difference is determined according to the following formula:
wherein said determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises:
the variable threshold is determined by the following formula:
δ＝0.1max(A(t))；
wherein δ represents a variable threshold;
a (t) represents an envelope of the upstream echo signal or the downstream echo signal;
wherein, A (t) is determined by the following formula:
x (t) represents an upstream or downstream signal:
wherein, X (t) is determined by the following formula:
wherein,the convolution of x (t) and 1/pi t is expressed as
Wherein H [ x (t) ] represents the Hilbert transform of x (t);
wherein said determining the transit time of the upstream ultrasonic signal and the transit time of the downstream ultrasonic signal based on the variable threshold comprises:
determining a maximum value of the upstream echo signal or the downstream echo signal envelope rising phase;
the local maximum point is determined by the following formula:
nn 0 ＝O+δ；
wherein nn 0 Representing local maximum point Z 0 Is the ordinate of (2);
delta represents a variable threshold;
o represents the minimum difference between the variable threshold and the ordinate of the maximum value of the envelope rise phase;
wherein, O is determined by the following formula:
O＝min(|δ-nn i |)；
wherein nn i Representing the i-th local maximum Z i Is the ordinate of (2);
by applying to said local maximum point Z 0 Two adjacent sampling points S -1 ，S +1 Performing parabolic interpolation processing on the three points to obtain a peak value;
determining the peak value as an upstream feature point or a downstream feature point S p (m p ,n p )；
Determining the transit time of the upstream echo signal or the downstream echo signal according to the following formula:
T u ＝T p +T u ’；
T d ＝T p +T d ’；
wherein T is P Representing the fixed time from the sending of the upstream ultrasonic signal or the downstream ultrasonic signal to the receiving of the upstream echo signal or the downstream echo signal, wherein the fixed time is obtained according to experiments;
T u ' represents the time from the start of sampling of the upstream echo signal to the upstream feature point;
T d ' represents the time from the start of sampling of the downstream echo signal to the downstream feature point,
wherein the T is d ' is determined by the following formula:
T d ’＝m p1 /Fs；
wherein m is p1 Representing downstream feature points S p1 Is the abscissa of (2);
fs represents the sampling rate at which the sample is taken,
wherein the T is u ' is determined by the following formula:
T u ’＝m p2 /Fs；
wherein m is p2 Representing upstream feature points S p2 Is defined by the abscissa of the (c).
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