CN101556173A - Coriolis mass flowmeter digital resolver based on wavelet de-noising and method thereof - Google Patents

Abstract

The invention relates to a coriolis mass flowmeter digital resolver based on wavelet de-noising and a method thereof. The key point of a coriolis mass flowmeter lies in that the frequency of vibration and phase difference (or time difference between two signals can be accurately measured; although a hardware circuit can be used for realizing the measuring function, the function which is realized by the hardware circuit is limited due to various technical reasons. The invention is characterized in that a temperature sensor can be used for sensing the fluid temperature and converting the fluid temperature into temperature electrical signal which is converted into digital signal by a signal conditioning circuit and an A/D converter, the digital signal is sent into a digital signal processor to be processed, and the mass, the flow rate and the density of the measured fluid are compensated. The invention widens the measuring range of the coriolis mass flowmeter and improves the accuracy of zero mark as well as the measuring accuracy of the flowmeter. Furthermore, the temperature sensor can be used for compensating the obtained mass, flow rate and density of the fluid, thus ensuring the accuracy of data.

Description

A kind of Coriolis mass flowmeter digital resolver and method based on wavelet de-noising

Technical field

The present invention relates to a kind of Coriolis mass flowmeter digital resolver and method based on wavelet de-noising.

Technical background

The device that the measuring tube that utilizes the former reason of Coriolis (Coriolics) to vibrate is measured the mass rate and the density of the fluid in the flowing pipe becomes coriolis mass flowmeters, in the U.S. Pat of authorizing people such as J.E.Smith-4109524 (on 08 29th, 1978), the ultimate principle and the method for relevant this flowmeter are disclosed among US-4491025 (on 01 01st, 1985) and the Re.31450 (02 month 11 days nineteen eighty-two), its key is the accurately frequency of measuring vibrations and the phase differential (or mistiming) of two paths of signals, though can realize such function with hardware circuit, the function that realizes with hardware circuit owing to various technical reasons is limited.

Current signal Processing for frequency and phase differential has following several method.

The U.S. Pat-4934196 (06 month 19 days nineteen ninety) of authorizing Romano has adopted variable sample frequency, make the data block of carrying out discrete time Fourier transform (DTFT) comprise an integer vibration period, thereby avoid non-integer to block the spectral leakage that is caused, but it has increased the complicacy of hardware circuit, and owing to need the real time altering sample frequency, real-time is just poor, if and error appears in the precision of track algorithm, will cause whole measuring accuracy deviation largely to occur.

Authorize the mode that Chris's bridge spy's of German Endress+Hauser Flowtec AG Chinese patent CN-1455859A (09 month 05 day calendar year 2001) has adopted hardware to combine with software, control the ratio of the two paths of signals that enters differential amplifier by DSP, make differential signal and reference signal quadrature, thereby resolve phase differential by differential wave and reference signal.

Authorize among the U.S. Pat P 580474 method that proposes to calculate the phase differential between the sensor two-way output signal of Coriolis flowmeter with digital phase-locked loop.The real-time that this method has frequency-tracking, phase difference calculating is good, frequency-tracking to random noise, fixed frequency disturb all have stronger inhibiting effect and phasometer to get it right inhibition that fixed frequency disturbs is also more intense; But compare with the ALE method, the ability that this method suppresses random noise a little less than, required sampling number is more, adopts the fixed sampling frequency time error bigger, this has just limited its application in coriolis mass flowmeters.

Authorize the fundamental frequency that the H.V of U.S. Micro Motion, Inc Derby, T. ripple west and S. draw refined Chinese patent CN-1190461A (on 08 12nd, 1998) to adopt the self-adaptation line wave filter (ANF) that strengthens (ALE) based on adaptive line to suppress various interference and try to achieve signal, again by the single-frequency point Fourier coefficient of Goertzel algorithm computation signal on fundamental frequency.And the Chinese patent CN-1467485A that authorizes Xu Ke army of HeFei University of Technology and Xu Wenfu has done improvement to the method: replace ANF with self-adaptation funnel type wave filter (AFF), can take into account frequency-tracking ability and tracking accuracy; Replace traditional Goertzel algorithm with slip Goertzel algorithm (SGA), the change sinusoidal signal also can be used the calculated signals fourier coefficient less than one-period when being fit to.This method can guarantee that transmitter follows the tracks of the variation of upper frequency under higher accuracy requirement, improve the signal to noise ratio (S/N ratio) of signal, we are exactly under the prerequisite with reference to its thinking, propose wavelet de-noising and combine better filtering noise with auto adapted filtering, improve the performance index of flowmeter.

Summary of the invention

The object of the present invention is to provide a kind of Coriolis mass flowmeter digital resolver and method based on wavelet de-noising, with the digital signal processor is that core adopts wavelet de-noising and adaptive trap filter to combine, to reduce noise, enhancing signal, tracking and measuring-signal frequency, widen the range of application of flowmeter survey; Adopt cross-correlation method, to measure the phase differential of two paths of signals.

For achieving the above object the technical scheme that the present invention takes:

The present invention includes the coriolis mass flowmeters body and contain the measuring tube of vibration, be arranged on two-way vibration transducer and signal conditioning circuit thereof on the measuring tube, A/D converter, controller, flash, LCD, vibration transducer is responded to the vibration of said measuring tube and is converted thereof into the speed electric signal, electric signal is transformed into digital signal through said signal conditioning circuit and said A/D converter, rate signal is sent into said digital signal processor, rate signal is wherein calculated the phase differential of vibration frequency and two paths of signals by said software algorithm in said digital signal processing, obtain the mass rate and the density of measured fluid thus, its special character is: also comprise the temperature sensor that is arranged on the measuring tube, digital signal processor, the temperature sensor senses fluid temperature (F.T.) also converts thereof into temperature signal, electric signal is transformed into digital signal through signal conditioning circuit and A/D converter, digital signal is sent into digital signal processor and is handled, and the mass rate and the density of measured fluid is compensated.

Above-mentioned digital filter adopts the sef-adapting filter based on lattice type IIR trapper, and it is formed by the dual stage filter cascade.

The method of resolving based on the Coriolis mass flowmeter digital of wavelet de-noising is: described digital signal is sent into digital signal processor and is handled through wavelet de-noising, digital filter successively, digital signal after the processing is carried out the cross-correlation method phase difference calculating, data are sent into the digital signal processing resolver, draw the mass rate and the density of measured fluid thus.

Above-mentioned wavelet de-noising may further comprise the steps:

A, wavelet decomposition, the highest level N of selection small echo and decomposition, signal calculated is at the wavelet coefficient of N layer;

B, set the threshold values of each layer details,, select threshold values, the wavelet coefficient of each layer details is handled with the threshold values method the 1st layer of each layer to the N layer;

C, reconstruction signal, for small echo, utilize the approximate part wavelet coefficient of N layer and from the 1st layer to treated details wavelet coefficient of N layer reconstruction signal.

Beneficial effect of the present invention:

The present invention adopt adaptive notch filter can be under the higher environment of signal to noise ratio (S/N ratio) filtering noise effectively, measuring accuracy, repdocutbility and the zero stability of coriolis mass flowmeters are improved; But because Coriolis flowmeter is based on the work of fluid oscillation principle, thereby noise effect is serious, the bandwidth of noise is bigger, wherein the power frequency of 50HZ disturb and influence of harmonic especially serious, our frequency that can not eliminate some man-made noises of industry spot fully drops between the frequency range of useful signal simultaneously.Under the lower situation of this signal to noise ratio (S/N ratio), adaptive algorithm is dispersed easily and is caused the inefficacy of wave filter, therefore the present invention introduces wavelet de-noising and makes coriolis mass flowmeters still have good performance in Testing of Feeble Signals before wave filter, the adding of wavelet de-noising is to the not influence of rate of convergence of adaptive notch filter, and the raising owing to signal to noise ratio (S/N ratio) behind the wavelet de-noising makes the convergence precision of adaptive notch filter that bigger improvement arranged on the contrary.Thereby widened the range of coriolis mass flow meter measurement, improved the precision of flowmeter Zero calibration simultaneously, the measuring accuracy that has improved.And added temperature sensor the mass rate and the density of the fluid that draws is compensated, guaranteed the accuracy of data.

Description of drawings

Fig. 1 is a system chart of the present invention;

Fig. 2 is the sef-adapting filter structural drawing of lattice type IIR trapper;

Fig. 3 is an adaptive notch filter Frequency Estimation relative error;

Fig. 4 is a signal time-domain diagram after the filtering;

Fig. 5 is a time-domain diagram after de-noising during 7dB under the heuristic threshold values principle;

Fig. 6 is a spectrogram after de-noising during 7dB under the heuristic threshold values principle;

Fig. 7 is under the heuristic threshold values principle-time-domain diagram after de-noising during 3dB;

Fig. 8 is under the heuristic threshold values principle-spectrogram after de-noising during 3dB;

Fig. 9 is that one-level extracts back signals and associated noises time-frequency figure;

Figure 10 is that one-level extracts back signals and associated noises spectrogram;

Figure 11 is signal time-frequency figure behind the wavelet de-noising;

Figure 12 is signal spectrum figure behind the wavelet de-noising;

Figure 13 is the normalized frequency convergence curve figure of adaptive notch filter;

Figure 14 is the frequency computation part relative error figure of adaptive notch filter;

Figure 15 is signal time-frequency figure behind the adaptive trap filter;

Figure 16 is signal time-frequency figure behind the adaptive trap filter.

Embodiment

The present invention is described in detail below in conjunction with the drawings and specific embodiments.

Device of the present invention comprises that the coriolis mass flowmeters body contains the measuring tube of vibration, be arranged on two-way vibration transducer and temperature sensor and signal conditioning circuit thereof on the measuring tube, A/D converter, controller, flash, LCD, digital signal processor and software algorithm wherein, vibration transducer is responded to the vibration of said measuring tube and is converted thereof into the speed electric signal, the temperature sensor senses fluid temperature (F.T.) also converts thereof into temperature signal, electric signal is transformed into digital signal through signal conditioning circuit and A/D converter, rate signal is sent into said digital signal processor, rate signal is wherein calculated the phase differential of vibration frequency and two paths of signals by said software algorithm in said digital signal processing, obtain the mass rate and the density of measured fluid thus, controller is sampled to said temperature signal, handle to said digital signal processor the data transmission after the sampling, the mass rate and the density of measured fluid is compensated.

The method of resolving based on the Coriolis mass flowmeter digital of wavelet de-noising is: digital signal is sent into digital signal processor and is handled through wavelet de-noising, digital filter successively, digital signal after the processing is carried out the cross-correlation method phase difference calculating, data are sent into the digital signal processing resolver, draw the mass rate and the density of measured fluid thus.

Wavelet de-noising may further comprise the steps:

1, wavelet decomposition, the highest level N of selection small echo and decomposition, signal calculated is at the wavelet coefficient of N layer;

2, set the threshold values of each layer details,, select threshold values, the wavelet coefficient of each layer details is handled with the threshold values method the 1st layer of each layer to the N layer;

3, reconstruction signal, for small echo, utilize the approximate part wavelet coefficient of N layer and from the 1st layer to treated details wavelet coefficient of N layer reconstruction signal.

Referring to Fig. 2, digital filter of the present invention adopts the sef-adapting filter based on lattice type IIR trapper, and it is formed by the dual stage filter cascade.

The transport function of this wave filter is

$H\left(z\right)=H_1\left(z\right)H_2\left(z\right)=\frac{1+k_0(1+k_1)z^{-1}+k_1{z}^{-2}}{1+a_0(1+a_1)z^{-1}+a_1{z}^{-2}}$

The sef-adapting filter of lattice type IIR trapper has different implementation methods, what the present invention adopted is that the Burg algorithm is realized, the Burg algorithm is based upon the efficient algorithm that the AR coefficient on the Fundamentals of Mathematics is found the solution, the order front and back are minimum to the predicated error sum, make this algorithm that The better resolution be arranged, its detailed process that realizes the self-adaptation adjustment is as follows:

ρ(n)＝0.998-0.195×0.99 ^(n-1)

λ(n)＝1-0.05×0.99 ^(n-1)

$s\left(n\right)=x\left(n\right)-{\hat{k}}_0(n-1)[1+\mathrm{\ρ}\left(n\right)]s(n-1)-\mathrm{\ρ}\left(n\right)s(n-2)$

D(n)＝λ(n)D(n-1)+2[1-λ(n)]s ²(n-1)

C(n)＝λ(n)C(n-1)+[1-λ(n)]s(n-1)[s(n)+s(n-2)]

${\hat{k}}_0\left(n\right)=-C\left(n\right)/D\left(n\right)---\left(1\right)$

Wherein, λ is a forgetting factor.Stable for guaranteeing wave filter, k ₀Must therefore in algorithm, add following detection link in [1,1], stable to guarantee algorithm.

${\hat{k}}_0\left(n\right)=\left\{\begin{array}{cc}{\hat{k}}_0\left(n\right)& -1\&le;{\hat{k}}_0\left(n\right)\&le;1\\ 1& {\hat{k}}_0\left(n\right)>1\\ -1& {\hat{k}}_0\left(n\right)<-1\end{array}---\left(2\right)\right.$

${\hat{k}}_0\left(n\right)=\mathrm{\&gamma;}{\hat{k}}_0(n-1)+(1-\mathrm{\&gamma;}){\hat{k}}_0\left(n\right)---\left(3\right)$

Formula (3) is equivalent to a low-pass filter, to what obtain

Carry out smoothing processing, choose γ=0.5.

The output of lattice type IIR trapper

$y\left(n\right)=s\left(n\right)+2{\hat{k}}_0\left(n\right)s(n-1)+s(n-2)---\left(4\right)$

At last, x (n)-y (n) is the enhancing signal behind the removal noise, and the Frequency Estimation of signal is then calculated by following formula

$\widehat{\mathrm{\&omega;}}\left(n\right)=\arccos (-{\hat{k}}_0\left(n\right))---\left(5\right)$

For checking its algorithm effects, it has been carried out simulation calculation.Wherein relative error by formula:

$\mathrm{err}=\frac{\widehat{\mathrm{\&omega;}}-\mathrm{\&omega;}}{\mathrm{\&omega;}}---\left(6\right)$

Calculate, its simulation result is shown in Fig. 3,4.

As can be seen from Figure 3, algorithm is located to restrain at 1500, and speed of convergence is very fast, and after convergence, the relative error of Frequency Estimation is a definite value substantially; Provided signal among Fig. 4 through the time-domain diagram after the filtering, as can be seen from Figure 4, after the sef-adapting filter of signal through lattice type IIR trapper, up to about 5000 o'clock, the amplitude of signal just approaches actual value.

The sef-adapting filter of lattice type IIR trapper can be under the higher environment of signal to noise ratio (S/N ratio) filtering noise effectively, measuring accuracy, repdocutbility and the zero stability of coriolis mass flowmeters are improved; But under the lower situation of signal to noise ratio (S/N ratio), adaptive algorithm is dispersed easily and is caused the inefficacy of wave filter, so the present invention introduces wavelet de-noising and makes coriolis mass flowmeters still have good performance in Testing of Feeble Signals before wave filter.

What the present invention selected for use is the absolute value of wavelet coefficient and the soft threshold values quantization method that threshold values compares; The threshold values principle adopts heuristic threshold values principle, Fig. 5～Fig. 8 provided use heuristic threshold values principle to the signal to noise ratio (S/N ratio) of signal be 7dB and-noise reduction during 3dB.

Wavelet de-noising cooperates utilization with adaptive trap filter, shown in Fig. 9～12: there is burr in signal as can be seen in time-domain diagram, but by behind the noise reduction from the signal time-domain diagram as can be seen, burr obviously minimizing improves than the noise reduction front signal, shown in Figure 13～14: the adding of wavelet de-noising is to the not influence of rate of convergence of adaptive notch filter, and still the raising owing to signal to noise ratio (S/N ratio) behind the wavelet de-noising makes the convergence precision of adaptive notch filter that bigger improvement arranged.

Referring to Figure 15～16, after the sef-adapting filter of signal through lattice type IIR trapper, the filter effect of noise is better, and the noise of low-frequency range and high band has all filtered out, as can be seen, the signal after the adaptive notch is a comparatively pure sinusoidal signal from the frequency spectrum of signal.

Claims (4)

1, a kind of Coriolis mass flowmeter digital resolver based on wavelet de-noising, comprise that the coriolis mass flowmeters body contains the measuring tube of vibration, be arranged on two-way vibration transducer and signal conditioning circuit thereof on the measuring tube, A/D converter, controller, flash, LCD, vibration transducer is responded to the vibration of said measuring tube and is converted thereof into the speed electric signal, electric signal is transformed into digital signal through said signal conditioning circuit and said A/D converter, rate signal is sent into said digital signal processor, rate signal is wherein calculated the phase differential of vibration frequency and two paths of signals by said software algorithm in said digital signal processing, obtain the mass rate and the density of measured fluid thus, it is characterized in that: also comprise the temperature sensor that is arranged on the measuring tube, digital signal processor, the temperature sensor senses fluid temperature (F.T.) also converts thereof into temperature signal, electric signal is transformed into digital signal through signal conditioning circuit and A/D converter, digital signal is sent into digital signal processor and is handled, and the mass rate and the density of measured fluid is compensated.

2, a kind of Coriolis mass flowmeter digital resolver based on wavelet de-noising according to claim 1 is characterized in that: described digital filter adopts the sef-adapting filter based on lattice type IIR trapper, and it is formed by the dual stage filter cascade.

3, the method for a kind of Coriolis mass flowmeter digital resolver based on wavelet de-noising according to claim 1, it is characterized in that: described digital signal is sent into digital signal processor and is handled through wavelet de-noising, digital filter successively, digital signal after the processing is carried out the cross-correlation method phase difference calculating, data are sent into the digital signal processing resolver, draw the mass rate and the density of measured fluid thus.

4, the method for a kind of Coriolis mass flowmeter digital resolver based on wavelet de-noising according to claim 3, it is characterized in that: described wavelet de-noising may further comprise the steps:

A, wavelet decomposition, the highest level N of selection small echo and decomposition, signal calculated is at the wavelet coefficient of N layer;

B, set the threshold values of each layer details,, select threshold values, the wavelet coefficient of each layer details is handled with the threshold values method the 1st layer of each layer to the N layer;

C, reconstruction signal, for small echo, utilize the approximate part wavelet coefficient of N layer and from the 1st layer to treated each the details wavelet coefficient reconstruction signal of N layer.

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