CN102889926A - Ultrasonic wave anti-noise detection method and system - Google Patents

Abstract

The invention discloses an ultrasonic wave anti-noise detection method and an ultrasonic wave anti-noise detection system. The method comprises the following steps of: firstly, performing generalized time-frequency domain average analysis on an ultrasonic wave signal which is obtained by repeated measurement, and thus obtaining a time-frequency analysis chart; secondly, identifying time and frequency corresponding to an energy center in the time-frequency analysis chart; and finally, slicing at the frequency corresponding to the energy center along a time shaft, and thus obtaining the detected ultrasonic wave signal. The invention has the advantages that by using a generalized time-frequency domain average technology, the defects of propagation path deflection caused by an installation effect of an ultrasonic wave detection device in a speed field, a pipeline manufacturing process, energy attenuation of ultrasonic wave in gas and low ratio of sound speed to flow speed, channel gain variation caused by gas pressure fluctuation, acoustic interference caused by a gas pressure regulating device, and the like are overcome, so the detection accuracy of the ultrasonic wave is high.

Description

A kind of ultrasound wave anti-noise detection method and system

Technical field

The invention belongs to the ultrasonic signal detection field, be specifically related to a kind of ultrasound wave anti-noise detection method and system.

Background technology

Ultrasound wave has that frequency is high, wavelength is short, the diffraction phenomenon is little, particularly good directionality, can become ray and the characteristics such as direction propagation.Ultrasound wave can be propagated in various different media, and moderate with the interaction of propagation medium, the medium status information of the relevant ultrasonic propagation that is easy to carry about with one.As information carrier and form of energy, the combinations such as ultrasonic technology and other electronic technology, optical technology extensively are applied, and develop rapidly.In recent years, be used widely in fields such as ultrasonic flow rate measurement, distance/wall thickness measuring and Ultrasonic NDT owing to its security, robustness and satisfied precision make it based on hyperacoustic various application.

At present, most ultrasonic applications all are based on and estimate transmission time (Time of Arrival, TOA) or the flight time (Time of Flight, TOF) of ultrasound wave in medium.Yet the ultrasound echo signal in the above-mentioned application causes amplitude or waveform distortion etc. problem owing to disturbed by noise or other signals.Ultrasonic signal itself then shows very strong non-stationary, non-linear characteristics.Above factor often detects to TOA/TOF and brings difficulty, finally causes ultrasonic applications to realize.Up to the present, existing multi-signal treatment technology is applied in the middle of the ultrasonic applications, such as cross-correlation method, match tracing, Kalman filtering, method of estimation, wavelet transformation and empirical mode decomposition etc. based on model.Yet the noise in the signal and other interference components also are to cause above-mentioned these technology can not the hyperacoustic principal element of fine detection.

The general temporal evolution of the instantaneous frequency of non-stationary signal and energy, the fundamental purpose of time frequency analysis be exactly the research instantaneous frequency of signal content and amplitude/energy thereof the time become situation.Various time-frequency analysis technologies can provide the time domain of signal, the information of frequency domain simultaneously, but different Time-Frequency Analysis Method has different time frequency resolution and concentration of energy.Time-frequency analysis technology is various features in the detection signal well, but can't distinguish useful and useless information.

Summary of the invention

Technical matters to be solved by this invention provides a kind of ultrasound wave anti-noise detection method and system, by the ultrasonic signal to repeatedly measuring, carry out broad sense time-frequency domain average treatment, the impact of the various interference such as noise in the erasure signal obtains effectively, ultrasonic signal reliably.

For addressing the above problem, the present invention is achieved by the following scheme:

A kind of ultrasound wave anti-noise detection method comprises the steps:

(1) sets sample frequency and sampling number, record the ultrasound data of repeatedly measuring;

(2) respectively the ultrasound data of repeatedly measuring is carried out time-frequency conversion;

The time-frequency conversion result of the ultrasound data that (3) will repeatedly measure carries out superposed average, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix;

(4) utilize the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart;

(5) at the maximum frequency point of center of energy, along the time shaft section, obtain the maximum frequency place and be the ultrasonic signal that detects.

In the above-mentioned steps (1), the ultrasound data of sampling need pass through after analog to digital conversion step and the pre-filtering step successively, just goes on record.

The described time-frequency conversion of above-mentioned steps (2) is selected linearity, secondary and/or self-adaptation time-frequency conversion method.

A kind of ultrasound wave anti-noise detection system comprises such as lower unit:

Record cell according to sample frequency and the sampling number set, is recorded the ultrasound data that ultrasonic receiver is repeatedly measured;

The time-frequency conversion unit carries out time-frequency conversion to the ultrasound data of repeatedly measuring respectively;

Broad sense time-frequency domain averaging unit is carried out superposed average with the time-frequency conversion result of the ultrasound data repeatedly measured, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix;

The extrema-finding unit utilizes the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart;

The signal determining unit at the maximum frequency point of center of energy, along the time shaft section, obtains the maximum frequency place and is the ultrasonic signal that detects.

Above-mentioned ultrasound wave anti-noise detection system also further comprises AD conversion unit and pre-filtering unit, wherein AD conversion unit is carried out analog to digital conversion to the ultrasound data of sampling, and the data of pre-filtering unit after to analog to digital conversion are carried out sending into record cell after the pre-filtering and carried out record.

In the such scheme, described time-frequency conversion unit selects linearity, secondary and/or self-adaptation time-frequency conversion method that the ultrasonic signal of repeatedly measuring is carried out time-frequency conversion.

The present invention is based on broad sense time-frequency domain averaging and realize that ultrasonic signal detects.The first step is advanced with the average analysis of broad sense time-frequency domain repeatedly measuring ultrasonic signal, obtains its time frequency analysis figure.Corresponding time of center of energy and frequency among the second step identification time-frequency figure.When cut into slices the ultrasonic signal that obtains detecting along time shaft at this frequency place.

Compared with prior art, the present invention has following features:

1, the present invention can overcome installation effect that ultrasonic detection device distributes in velocity field, pipeline manufacturing process, the ultrasonic less travel path deflection that brings of energy attenuation, the velocity of sound/flow velocity ratio, the channel gain change that the gaseous tension fluctuation causes, the acoustic interference that gas pressure regulating apparatus causes in gas etc.;

2, the ultrasound wave time precision that detects of the present invention is high;

3, the present invention can be different types of ultrasonic applications device use such as ultrasonic flowmeter, supersonic diagnostic set, and therefore, the wide popularization and application that has is worth.

Description of drawings

Fig. 1 is the scheme of installation of the present invention in the ultrasonic gas flow velocity measuring system.

Fig. 2 is that broad sense time-frequency domain averaging and the ultrasound wave peak value when adopting SPWV, CWT and HHT detects schematic diagram (this schematic diagram only represents the averaging of time frequency analysis of the same race).

Fig. 3 (a)-(d) under different operating modes, carry out the time domain average analysis result for ultrasonic signal.

Fig. 4 (a1)-(c1) ultrasonic signal when P=0psig carries out broad sense time-frequency domain average analysis result, i.e. broad sense time-frequency domain mean chart.

Fig. 4 (a2)-(c2) is ultrasonic signal peak value slice map when P=0psig.

Embodiment

Be described in further detail below in conjunction with the content of accompanying drawing to the embodiment of tool of the present invention in ultrasonic flowmeter:

The ultrasonic flow detection technique is in recent years in one of instrument monitoring, control and fields of measurement technology with fastest developing speed.Ultrasonic flowmeter is divided into gas and liquid two large field types, both ultimate principles are identical, all utilize ultrasound wave respectively when mobile and static Propagation, with respect to fixed coordinate system (such as instrument housing), its velocity of propagation is discrepant, and the variable quantity of velocity of propagation is relevant with velocity of medium.Can obtain velocity of medium according to the variation of ultrasonic propagation velocity thus, under the prerequisite of known cross-sectional flow area and then obtain flow.Yet, because the various unfavorable factors of outwardness in the measurement of gas flow, comprise installation effect that velocity field distributes, pipeline manufacturing process, the ultrasonic less travel path deflection that brings of energy attenuation, the velocity of sound/flow velocity ratio, the channel gain change that the gaseous tension fluctuation causes, the acoustic interference that gas pressure regulating apparatus causes in gas etc., so that the ultrasonic gas flow detection is compared liquid is unusually difficult.

The present embodiment adopts the broad sense time-frequency domain on average the ultrasound wave in the ultrasonic flowmeter to be detected.

Clamp-mounting type (clamp-on) ultrasonic gas flow quantity detecting system is adopted in the collection of the present embodiment external ultrasonic signal, and its mounting structure as shown in Figure 2.A pair of ultrasonic generator and ultrasonic receiver are installed on the pipeline that diameter is 6 inches (approximately 152.4mm) face-to-face.The amplitude that can inspire certain frequency when ultrasound transmitter device A is triggered by monopulse is the vibration ultrasound wave of first increases and then decreases gradually, and this ultrasound wave is received by ultrasonic receiver B after penetrating pipeline.Although, experimental results demonstrate interference and the loss of signal of 500kHz resonant frequency energy noise decrease.But owing to be the intrinsic influence factor of clamp-mounting type and gas flow measurement, the problems such as signal to noise ratio (S/N ratio) is low so that the signal that receives still exists, waveform distortion.Particularly lower (such as 0psig at gaseous tension, 1psi=6.89kPa psig is gauge pressure here, 0psig represents that external and internal pressure equates, also be 1atm or 0.1MPa) and flow velocity when very fast signal interference problem even more serious, this brings great challenge to traditional ultrasonic detection method.

Gas velocity and air in pipeline pressure P are controlled by servomotor frequency (Motor Frequency, MF) and flow control valve respectively.Gas flow rate is faster in the larger corresponding system of MF numerical value, and the servomotor frequency is that the corresponding flow velocity of 60Hz(is about 121.6ft/s or 37.06m/s in the present embodiment).In addition, the temperature variation of gas can be brought impact to measuring-signal, so proving installation outfit cooling system can make temperature remain on about 80 ℉ (approximately 26.7 ℃).

Ultrasound wave anti-noise detection system in the computing machine is processed the signal that ultrasonic receiver collects according to following steps, and namely this implements described ultrasound wave anti-noise detection method as shown in Figure 2.

(1) sets sample frequency and sampling number, record the ultrasound data of repeatedly measuring.

In the present embodiment, the setting sample frequency is 20MHz, and sampling number is 2048 points.

(2) respectively the ultrasound data of repeatedly measuring is carried out time-frequency conversion.In the present invention, ultrasonic signal is carried out time-frequency conversion and can select linearity, secondary and/or self-adaptation time-frequency conversion method.

For signal s (t), can adopt linear time-frequency conversion method to have: Short Time Fourier Transform (STFT), continuous wavelet transform (CWT) etc.

If the employing Short Time Fourier Transform, the time-frequency conversion of signal s (t) is

$W_{\mathrm{STFT}}^{s,g}(t,f)=\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}s\left(\mathrm{\&tau;}\right)g^{*}(\mathrm{\&tau;}-t)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="DEST\_PATH\_HDA00002314123200011.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;f}\&CenterDot;\mathrm{\&tau;}}\mathrm{d\&tau;}$

Wherein, g (t) is institute's added-time window function.

If the employing wavelet transformation, then the time-frequency conversion of signal s (t) is

$W_{\mathrm{WT}}^{s,\mathrm{\&psi;}}(t,a)\stackrel{\mathrm{\&Delta;}}{=}\frac{1}{\sqrt{a}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}s\left(\mathrm{\&tau;}\right){\mathrm{\&psi;}}^{*}\left(\frac{t-\mathrm{\&tau;}}{a}\right)\mathrm{d\&tau;}$

Wherein, ψ is mother wavelet function.It is zero function in the time shaft upper integral that ψ is one, can get small echo atom ψ to ψ after the flexible and translation _{τ, a}(t)=a ^1/2((t-τ)/a), mother wavelet function choose one dimension Gabor small echo to ψ, and its expression formula is formula

$\mathrm{\&psi;}\left(t\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}{\mathrm{\&sigma;}}_t^2}}{e}^{-\frac{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DEST\_PATH\_HDA00002314123200011.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}{2{\mathrm{\&sigma;}}_t^2}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="DEST\_PATH\_HDA00002314123200011.png"\; state="\{\{state\}\}">e</figure-callout>}}^j$

Wherein, σ _tThe frequency span of expression small echo, f ₀Centre frequency for small echo.

For signal s (t), can adopt secondary time-frequency conversion method to have: Cohen class time-frequency distributions, smooth Wigner-Ville time-frequency distributions (SPWV) etc.

If adopt Cohen class time-frequency distributions, then the time-frequency conversion of signal s (t) is

$W_K^s(t,f)={\&Integral;}_{-\&infin;}^{+\&infin;}{\&Integral;}_{-\&infin;}^{+\&infin;}K(t,f;\mathrm{\&upsi;},\mathrm{\&tau;})s(t+\frac{\mathrm{\&tau;}}{2})s^{*}(t-\frac{\mathrm{\&tau;}}{2})\mathrm{d\&upsi;d\&tau;}$

Wherein, K (t, f; υ, τ) be called the kernel function that satisfies certain condition.

If adopt smooth pseudo-Wigner-Ville time-frequency distributions, then the time-frequency conversion of signal s (t) is

$W_{\mathrm{SPWV}}^{s,g,h}(t,f)\stackrel{\mathrm{\&Delta;}}{=}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}g(u-t)\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}h\left(\mathrm{\&tau;}\right)s(u+\frac{\mathrm{\&tau;}}{2})s^{*}(u-\frac{\mathrm{\&tau;}}{2})e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="DEST\_PATH\_HDA00002314123200011.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;f\&tau;}}\mathrm{d\&tau;du}$

G in the following formula (t) and h (t) are windowed function.The establishment cross term but smooth pseudo-Wigner-Ville distributes.

For signal s (t), can adopt self-adaptation time-frequency conversion method to have: Hilbert-Huang spectrum (HHS) etc.

If adopt the Hilbert-Huang spectrum, then the time-frequency conversion of signal s (t) is

Hilbert-Huang that instantaneous amplitude and instantaneous frequency are constructed spectrum (Hilbert-Huang Spectrum, HHS) can the concentrated expression signal characteristic information, and the Time-Frequency Information matrix can be obtained by following formula.

$W_{\mathrm{HHT}}^s(f,t)\stackrel{\mathrm{\&Delta;}}{=}{(f_i\left(t\right),a_i\left(t\right))}_{i=1,...,n,j=1,...,n}$

The time-frequency conversion result of the ultrasound data that (3) will repeatedly measure carries out superposed average, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix.The above-mentioned time-frequency conversion result who carries out superposed average can be the time-frequency conversion result who adopts same time-frequency transformation analysis method to obtain, and can be the time-frequency conversion result who adopts time-frequency transformation analysis method not of the same race to obtain.

By broad sense time-frequency average treatment, obtain the time-frequency figure after noise is eliminated.Namely

If s _i(t) be one group of time-domain signal in the N group measuring-signal,

S for this reason _i(t) the time-frequency conversion result of signal, T represent a certain time-frequency conversion that adopts, and it can be linear, secondary and adaptive Time Frequency Analysis method.For N group signal, the Time-Frequency Information matrix that obtains after time-frequency domain is average

For

${\stackrel{\&OverBar;}{W}}_T^s(t,f)=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{W}_T^{s_i}(t,f)$

Be smooth pseudo-Wigner-Ville when distributing if time-frequency conversion adopts, the average result of broad sense time-frequency domain is available

Expression.If time-frequency conversion adopts when being a certain time-frequency computing among SPWV, Scalogram or the HHS, correspondingly the average result of broad sense time-frequency domain can note by abridging respectively and be

With

If time-frequency conversion adopts wavelet transformation and two kinds of Time-frequency method analytic signals of Bilinear TFD s (t), will obtain the broad sense time-frequency domain averaging similar to formula and be this moment

${\stackrel{\&OverBar;}{W}}_{\mathrm{\&Xi;}\&cup;\mathrm{\&Omega;}}^s(t,f)=\frac{1}{J}\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{W}_{\mathrm{\&Xi;}}^{{\mathrm{\&Omega;}}_s(t,f^j)}(t,f)$

Wherein: Ξ ∪ Ω represents the joint time-frequency operation.

(4) utilize the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart;

(5) at the maximum frequency point of center of energy, along the time shaft section, obtain the maximum frequency place and be the ultrasonic signal that detects.

The following validity by concrete data verification said method:

At MF=60Hz and P=0psig(0.1Mpa), 5psig(0.134Mpa), 15psig(0.203Mpa) or the about 0.445Mpa of 50psig() in the situation, following current (being ultrasonic generator A → B direction among Fig. 2) gathers respectively 80 groups of data with adverse current (B → A direction).All data store in the computing machine after A/D conversion and near pre-filtering (500kHz).

Along with the increase of gaseous tension, the signal to noise ratio (S/N ratio) of following current and adverse current collection signal all is enhanced, the signal when collection signal is subjected to the impact of external interference to be less than adverse current during following current.Therefore, be subjected to extraneous interference larger at low pressure (such as P=0psig and 5psig), countercurrent direction signal, signal to noise ratio (S/N ratio) is lower.To time domain average technology (TDA) analysis result of 80 groups of data gathering under above-mentioned every kind of operating mode as shown in Figure 3, can find out when P=0psig and 5psig, TDA detects effect neither be desirable especially, and it is limited in one's ability when processing waveform distortion or have signal than the strong jamming composition that reason is the TDA technology.Therefore, the present embodiment adopts broad sense time-frequency domain averaging (ETFDA) technology to analyze mainly for above-mentioned P=0psig and two kinds of operating modes of 5psig, comes the validity of verification method.

AVSPWV, AVSG and AVHHS analysis result be respectively shown in Fig. 4 (a1), (b1), (c1) when p=0psig, can find out obviously that therefrom three kinds of ETFDA technology locate successfully to detect the ultrasonic signal (arrow indication among the figure) of following current and countercurrent direction in 500kHz frequency of operation (or yardstick 50).Fig. 4 (a2), (b2), (c2) show the 500kHz frequency place section of corresponding three time-frequency figure, and following current (solid line) all detects effectively with adverse current (dotted line) direction ultrasound wave.In such cases, corresponding A VSPWV, AVSG and the AVHHS technology for detection ultrasound wave moment point (dotted line represents among Fig. 4 (a2), (b2), (c2)) that goes out following current and countercurrent direction is respectively 611 and 868,611 and 869,609 and 862.Therefore, even three kinds of ETFDA technology still successfully detected ultrasound wave in the signal when there was strong interference component in signal, and the time is basically identical, and the mistiming is about 12.85us(257/20M).

A kind of ultrasound wave anti-noise detection system designed according to said method comprises such as lower unit:

AD conversion unit is carried out analog to digital conversion to the ultrasound data of sampling.

Pre-filtering unit, the pre-filtering unit data after to analog to digital conversion are carried out sending into record cell after the pre-filtering and are carried out record.

Record cell according to sample frequency and the sampling number set, is recorded the ultrasound data that ultrasonic receiver is repeatedly measured.

The time-frequency conversion unit carries out time-frequency conversion to the ultrasound data of repeatedly measuring respectively.Described time-frequency conversion unit selects linearity, secondary and/or self-adaptation time-frequency conversion method that the ultrasonic signal of repeatedly measuring is carried out time-frequency conversion.

Broad sense time-frequency domain averaging unit is carried out superposed average with the time-frequency conversion result of the ultrasound data repeatedly measured, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix.

The extrema-finding unit utilizes the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart.

The signal determining unit at the maximum frequency point of center of energy, along the time shaft section, obtains the maximum frequency place and is the ultrasonic signal that detects.

Above-described embodiment only is the specific case that purpose of the present invention, technical scheme and beneficial effect are further described, and the present invention is defined in this.All any modifications of within scope of disclosure of the present invention, making, be equal to replacement, improvement etc., all be included within protection scope of the present invention.

Claims (6)

1. a ultrasound wave anti-noise detection method is characterized in that comprising the steps:

(1) sets sample frequency and sampling number, record the ultrasound data of repeatedly measuring;

(2) respectively the ultrasound data of repeatedly measuring is carried out time-frequency conversion;

The time-frequency conversion result of the ultrasound data that (3) will repeatedly measure carries out superposed average, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix;

(4) utilize the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart;

(5) at the maximum frequency point of center of energy, along the time shaft section, obtain the maximum frequency place and be the ultrasonic signal that detects.

2. a kind of ultrasound wave anti-noise detection method according to claim 1, it is characterized in that: in the step (1), the ultrasound data of sampling need pass through after analog to digital conversion step and the pre-filtering step successively, just goes on record.

3. a kind of ultrasound wave anti-noise detection method according to claim 1 and 2, it is characterized in that: the described time-frequency conversion of step (2) is selected linearity, secondary and/or self-adaptation time-frequency conversion method.

4. ultrasound wave anti-noise detection system is characterized in that comprising such as lower unit:

Record cell according to sample frequency and the sampling number set, is recorded the ultrasound data that ultrasonic receiver is repeatedly measured;

The time-frequency conversion unit carries out time-frequency conversion to the ultrasound data of repeatedly measuring respectively;

Broad sense time-frequency domain averaging unit is carried out superposed average with the time-frequency conversion result of the ultrasound data repeatedly measured, obtains the Time-Frequency Information matrix, and generates broad sense time-frequency domain mean chart according to the Time-Frequency Information matrix;

The extrema-finding unit utilizes the extreme value finding method, corresponding time of center of energy and the frequency information of search broad sense time-frequency domain mean chart;

The signal determining unit at the maximum frequency point of center of energy, along the time shaft section, obtains the maximum frequency place and is the ultrasonic signal that detects.

5. a kind of ultrasound wave anti-noise detection system according to claim 4, it is characterized in that: also further comprise AD conversion unit and pre-filtering unit, wherein AD conversion unit is carried out analog to digital conversion to the ultrasound data of sampling, and the data of pre-filtering unit after to analog to digital conversion are carried out sending into record cell after the pre-filtering and carried out record.

6. it is characterized in that according to claim 4 or 5 described a kind of ultrasound wave anti-noise detection systems: described time-frequency conversion unit selects linearity, secondary and/or self-adaptation time-frequency conversion method that the ultrasonic signal of repeatedly measuring is carried out time-frequency conversion.

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