CN104677437A - Ultrasonic liquid phase flow rate precision measuring method - Google Patents

Abstract

The invention discloses an ultrasonic liquid phase flow rate precision measuring method. The method comprises the steps of transmitting a ultrasonic transmission signal by virtue of a transducer transmitting probe, scattering the transmission signal by virtue of solid particles in fluid in a pipeline, and receiving an echo signal by virtue of a transducer receiving probe; changing the frequency of the echo signal in a frequency mixer to obtain a medium-frequency signal; inputting the frequency-converted signal to a low-pass filter to be filtered; solving an echo average frequency; solving the fluid flow speed and the volume flow rate in the pipeline. By selecting the 2MHz ultrasonic transmission signal, the particles capable of returning the echo can be reduced, the flow rate information can be more comprehensively reflected by utilizing the motion state of the smaller particles, and the flow rate measurement error can be reduced; the flow rate signal is enable to appear in the low-frequency band in a frequency mixing way by virtue of the low-pass filter, the weaknesses of large calculation amount and long calculation time caused by the high sampling frequency when the signal is processed can be avoided, and the real-time property of the flow rate information and the accuracy for instantaneously measuring the flow rate can be improved.

Description

A kind of ultrasonic solution phase flow rate precision measuring method

Technical field

The invention belongs to electronic measuring technology field, relate to a kind of ultrasonic solution phase flow rate precision measuring method.

Background technology

Ultrasonic flow meter develops rapidly in general industry field, is mainly used in the aspects such as process monitoring, measurement and control.Ultrasonic flow is in respect of two kinds of main types: time difference method and Doppler method.Transit time ultrasonic flow meters has a transmitting probe and a receiving transducer.It sends two ultrasonic signals at pipe outer wall with an angle: a following current, an adverse current.Then measure " transmission time " of each signal.Ultrasound wave time difference method essence asks two the order of magnitude is relatively large and the time elementary errors that numerical value is close.For the situation that caliber is less, the accuracy of the time difference is more difficult to ensure card, and time difference method is suitable only for the measurement of Large Diameter Pipeline rate of flow of fluid.Doppler's flow measurement also belongs to non-contact measurement, and the modulation of ultrasonic signal containing solia particle or bubble in fluid produces Doppler effect, and echoed signal is just with the flow rate information (i.e. Doppler shift) of fluid.Ultrasound wave receiving transducer receives echoed signal, and treated circuit carries out transmission frequency and receive frequency mathematic interpolation and conditioning and then tries to achieve flow velocity.Doppler Ultrasonic Flowmeter is suitable for the measurement to the liquid phase fluid flow velocity containing solia particle or bubble.

Because the frequency displacement of Doppler method is difficult to treatment and analysis, algorithmically relative time error method more complicated, so the measuring accuracy of Doppler method is lower than time difference method measuring accuracy, commercial Application at home and abroad almost be can't see the ultrasonic flow meter of Doppler method.Substantially be limited as the not high occasion of accuracy requirement in the occasion of using ultrasound ripple Doppler flowmeter abroad, such as, when measuring blood flow, because the precision needed is not high, demonstrate blood flow and indicate just passable dynamically, be similar to the fluctuation display of cardiogram one class.

Summary of the invention

The object of this invention is to provide a kind of ultrasonic solution phase flow rate precision measuring method, solve the problem that existing doppler flow measuring method precision is low, error is large.

The technical solution adopted in the present invention is, a kind of ultrasonic solution phase flow rate precision measuring method, specifically implements according to the following steps:

Step 1, transducer transmitting probe is launched ultrasound wave and is transmitted, and transmits by the solid particle scattering in fluids within pipes, and receive MUT probe receives echoed signal;

Step 2, frequency mixer frequency conversion:

The echoed signal received is converted to electric signal by receive MUT probe, and carries out difference frequency by the signal input mixer of itself and certain frequency, obtains intermediate-freuqncy signal;

Step 3, by filtering in the signal input low-pass filter after frequency conversion;

Step 4, asks for echo average frequency;

Step 5, asks for rate of flow of fluid and volumetric flow rate in pipeline.

Feature of the present invention is also,

The ultrasound wave emission signal frequency that wherein in step 1, transducer transmitting probe is launched is 2MHz.

In frequency mixer, wherein carry out emission signal frequency described in the frequency of the signal of difference frequency and step 1 in step 2 with electric signal identical.

Wherein ask for echo average frequency in step 4, be specially:

Process in filtered signal input processor, use FFT frequency shift signal sequence to carry out sampled-data estimation to power spectrum, the average frequency of trying to achieve echo is:

${\stackrel{\‾}{f}}_{\mathrm{\Δ}}=\frac{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}{f}_{K}p\left(K\right)}{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}p\left(K\right)},$

Wherein, for the average frequency of echo, p (K) is power spectrum.

Wherein ask for rate of flow of fluid and volumetric flow rate in pipeline in step 5, be specially

Frequency displacement relation according to Doppler effect:

$u=\frac{{\stackrel{\‾}{f}}_{\mathrm{\Δ}}v}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}},$

Wherein, u is the speed of solid particle along pipe axial-movement, and v is the velocity of propagation transmitted, and α is the angle of v and u, then actual internal area is in the pipeline of A, and the volumetric flow rate of fluid is:

$Q=\frac{\mathrm{Av}}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}}{\stackrel{\‾}{f}}_{\mathrm{\Δ}}.$

The invention has the beneficial effects as follows, a kind of ultrasonic solution phase flow rate precision measuring method, selected frequency is that the ultrasound wave of 2MHz transmits and makes the particle that can be used for reflection echo less, to utilize the motion state compared with small-particle more, more fully reflect that flow rate information reduces fluid-velocity survey error; Flow velocity signal is made to appear at low-frequency range in the mode of mixing through low-pass filter, the shortcoming that when avoiding ultrasonic signal process near 2MHz, too high the brought calculated amount of sample frequency is large, operation time is long, also improve the real-time of flow rate information and the accuracy of instantaneous delivery measurement simultaneously, in the signal transacting improving industrial fluid-mixing flow measurement precision, there is positive role to Doppler flowmeter.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of a kind of ultrasonic solution phase flow rate of the present invention precision measuring method;

Fig. 2 is the sound scattering schematic diagram of a kind of ultrasonic solution phase flow rate of the present invention precision measuring method.

In figure, 1. pipeline, 2. transducer transmitting probe, 3. receive MUT probe, 4. transmits, 5. echoed signal, 6. solid particle.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

The invention provides a kind of ultrasonic solution phase flow rate precision measuring method, as shown in Figure 1, concrete steps are:

Step 1, as shown in Figure 2, adopt frequency to be that the transducer transmitting probe 2 of 2MHz is launched ultrasound wave and transmitted 4, transmit 4 by solid particle 6 scattering in pipeline 1 inner fluid, receive MUT probe 3 receives echoed signals 5;

Step 2, frequency mixer frequency conversion:

The echoed signal 5 received 3 is converted to electric signal by receive MUT probe, and carries out difference frequency by the signal input mixer of itself and 2MHz frequency, obtains intermediate-freuqncy signal;

Step 3, by filtering in the signal input low-pass filter after frequency conversion;

Step 4, ask for echo average frequency:

Process in filtered signal input dsp chip TMS320F2812, use FFT frequency shift signal sequence to carry out sampled-data estimation to power spectrum, the average frequency of trying to achieve echo is:

${\stackrel{\‾}{f}}_{\mathrm{\Δ}}=\frac{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}{f}_{K}p\left(K\right)}{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}p\left(K\right)},$

Wherein, for the average frequency of echo, p (K) is power spectrum.

Step 5, asks for rate of flow of fluid and volumetric flow rate in pipeline.

According to Doppler effect frequency displacement relation:

$u=\frac{{\stackrel{\‾}{f}}_{\mathrm{\Δ}}v}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}},$

Wherein, u is the speed of solid particle 6 along pipe axial-movement, v be transmit 4 velocity of propagation, α is the angle of v and u, then actual internal area is in the pipeline of A, and the volume flow Q of fluid is:

$Q=\frac{\mathrm{Av}}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}}{\stackrel{\‾}{f}}_{\mathrm{\Δ}}.$

In ultrasound wave precision measuring channel of the present invention, the principle of fluid flow is:

The frequency relation of Doppler effect is:

$f_1=\left(\frac{v\±v_0}{v\stackrel{\‾}{+}{v}_s}\right)f---\left(1\right)$

F ₁for the frequency observed; F launches the original transmitted frequency come from this medium; V is ripple gait of march in the medium; v ₀for observer's translational speed, if close to emissive source, front sign of operation is+number, otherwise be then-number; v _sfor emissive source translational speed, if close to observer, front sign of operation is-number, otherwise be then+number.

As shown in Figure 2, run into the solid particle 6 of speed u along pipeline 1 axial-movement in ultrasonic signal 4 is propagated with speed v, relative to transducer transmitting probe 2, solid particle 6 far goes with ucos α speed, so the ultrasonic frequency that receives of solid particle 6 should lower than transmit 4 frequency f, according to (1) formula, the ultrasonic frequency that solid particle 6 receives is:

$f^{\′}=\left(\frac{v-u\cos \mathrm{\α}}{v}\right)f---\left(2\right)$

And solid particle 6 is by ultrasonic beam scattering, and received by receive MUT probe 3, because solid particle 6 leaves receive MUT probe 3 with the speed of ucos α, so the ultrasonic frequency that receive MUT probe 3 receives reduces again, according to the ultrasonic frequency that (1) formula receive MUT probe 3 receives be:

$f_1=\left(\frac{v}{v+u\cos \mathrm{\α}}\right)f^{\′}=\left(\frac{v-u\cos \mathrm{\α}}{v+u\cos \mathrm{\α}}\right)f---\left(3\right)$

So, obtain the Doppler shift of individual reflection ripple:

$\mathrm{\Δf}=f-f_1=\frac{2u\cos \mathrm{\α}}{v+u\cos \mathrm{\α}}f---\left(4\right)$

This method is applicable to the occasion of single echo, but in reality, doppler echo is not single, is difficult to try to achieve Δ f by simple way.In addition, the relative motion of each particle is again uncertain, and as shown in Figure 2, actual motion direction such as the solid line in figure of hypothetical particle represents, and required flow velocity direction is the direction of u in figure, therefore adopts power spectrum to ask the average frequency of doppler echo.

The signal that receive MUT probe 3 receives is that the aliasing of multiple Doppler shift composition causes random noise with some uncertain factors, and the signal form detected can be expressed as:

Wherein, s ₁t () is through the non-athletic such as tube wall and lining medium couples to the signal accepting probe, s ₂t () is echo component, r (t) is external interference and the probabilistic random noise of change of flow state, and t is the time, a ₀for signal width position, for phase place, ω ₀for the frequency transmitted, a _ifor the amplitude of echo component, (ω ₁) _ifor the frequency of echo component, for the phase place of echo component.

Power spectrum is adopted to ask the average frequency of Doppler's scattering wave to be:

${\stackrel{\‾}{f}}_{\mathrm{\Δ}}=\frac{{\∫}_0^{\∞}{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\·p\left({\stackrel{\‾}{f}}_{\mathrm{\Δ}}\right)d{\stackrel{\‾}{f}}_{\mathrm{\Δ}}}{{\∫}_0^{\∞}p\left({\stackrel{\‾}{f}}_{\mathrm{\Δ}}\right)d{\stackrel{\‾}{f}}_{\mathrm{\Δ}}}---(6-1)$

Wherein, for power spectrum, for the average frequency of echo.

Sample at certain temporal interval, simulating signal become digital signal (sequence), then carry out discrete time Fourier transform, obtain the average frequency calculating formula of the echo of discretize:

${\stackrel{\‾}{f}}_{\mathrm{\Δ}}=\frac{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}{f}_{K}p\left(K\right)}{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}p\left(K\right)}---(6-2)$

Wherein, p (K) is power spectrum.

Obtained by (4) formula, the flow velocity of fluids within pipes is:

$u=\frac{{\stackrel{\‾}{f}}_{\mathrm{\Δ}}v}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}}---\left(7\right)$

When then the actual internal area of pipeline 1 is A, then volume flow Q:

$Q=\frac{\mathrm{Av}}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}}{\stackrel{\‾}{f}}_{\mathrm{\Δ}}---\left(8\right)$

Foundation sound wave in a liquid velocity of propagation approximately gets v ≈ 1000m/s, can draw λ ≈ 5 × 10 by f=2Mhz ^-4m.Known 4 frequencies that transmit are larger, the size of ultrasound wave identification solid particle 6 is less, namely transmit and 4 to the solid particle 6 that size is greater than decimillimeter rank, diffraction phenomenon can not occur, thus select the ultrasound wave of frequency 2MHz to transmit and 4 improve identification to fine particle in measuring process, receive MUT is popped one's head in and 3 more can collect the flow rate information that various sizes solid particle 6 feeds back.

Because local frequency and echo frequency easily meet close to dynamic range, the present invention selects the 2MHz frequency signal identical with transmission frequency and echoed signal to carry out difference frequency.Because conversion process requires low, as long as to each frequency content signal attenuation of intermediate-freuqncy signal unanimously for conversion loss; And in subsequent step, have low-pass filter to carry out signal transacting, and therefore also very low to frequency mixer insulated degree requirement, so general frequency mixer just can directly be selected in conversion process.

Frequency signal after difference frequency is adopted to the frequency signal of low-pass filter filtering high band, make frequency shift signal in low-frequency range, avoid the shortcoming that calculated amount is large, operation time is long that when signal is sampled on high band, sample frequency height brings, improve the real-time of flow rate information, namely improve the accuracy of instantaneous delivery.

Claims (5)

1. a ultrasonic solution phase flow rate precision measuring method, is characterized in that, specifically implements according to the following steps:

Step 1, transducer transmitting probe is launched ultrasound wave and is transmitted, and transmits by the solid particle scattering in fluids within pipes, and receive MUT probe receives echoed signal;

Step 2, frequency mixer frequency conversion:

The echoed signal received is converted to electric signal by receive MUT probe, and carries out difference frequency by the signal input mixer of itself and certain frequency, obtains intermediate-freuqncy signal;

Step 3, by filtering in the signal input low-pass filter after frequency conversion;

Step 4, asks for echo average frequency;

Step 5, asks for rate of flow of fluid and volumetric flow rate in pipeline.

2. a kind of ultrasonic solution phase flow rate precision measuring method according to claim 1, is characterized in that, the ultrasound wave emission signal frequency that in described step 1, transducer transmitting probe is launched is 2MHz.

3. a kind of ultrasonic solution phase flow rate precision measuring method according to claim 1, is characterized in that, in frequency mixer, carry out emission signal frequency described in the signal frequency of difference frequency and step 1 in described step 2 with electric signal identical.

4. a kind of ultrasonic solution phase flow rate precision measuring method according to claim 1, is characterized in that, ask for echo average frequency, be specially in described step 4:

Process in filtered signal input processor, use FFT frequency shift signal sequence to carry out sampled-data estimation to power spectrum, the average frequency of trying to achieve echo is:

${\stackrel{\‾}{f}}_{\mathrm{\Δ}}=\frac{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}{f}_{K}p\left(K\right)}{\underset{K=0}{\overset{N-1}{\mathrm{\Σ}}}p\left(K\right)},$

Wherein, for the average frequency of echo, p (K) is power spectrum.

5. a kind of ultrasonic solution phase flow rate precision measuring method according to claim 1, is characterized in that, ask for rate of flow of fluid and volumetric flow rate in pipeline, be specially in described step 5

Frequency displacement relation according to Doppler effect:

$u=\frac{{\stackrel{\‾}{f}}_{\mathrm{\Δ}}v}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}},$

Wherein, u is the speed of solid particle along pipe axial-movement, and v is the velocity of propagation transmitted, and α is the angle of v and u, then actual internal area is in the pipeline of A, and the volume flow Q of fluid is:

$Q=\frac{\mathrm{Av}}{2f\cos \mathrm{\α}-{\stackrel{\‾}{f}}_{\mathrm{\Δ}}\cos \mathrm{\α}}{\stackrel{\‾}{f}}_{\mathrm{\Δ}}.$