CN1804557A - Signal processing method of propagation speed differential type ultrasonic flowmeter - Google Patents

Abstract

The invention relates to a signal processing method of propagation speed difference type ultrasonic flow meter used to measure the propagation time in measuring pipe of ultrasonic signal so as to measure the speed of the flow. The method comprises: (1) using coding modulating ultrasonic signal with self-relative character to generate the sending signal; (2) carrying the flow information by pipe flow field propagation by the sending signal; (3) receiving the sending signal with flow information and doing relative computing with the sending signal of the step one; (4) measuring the propagation time of the ultrasonic signal by the peak location of the relative function to compute the speed of the flow.

Description

The signal processing method of propagation speed differential type ultrasonic flowmeter

Technical field

The invention belongs to the ultrasonic flow meter category, particularly a kind of signal processing method of ultrasonic flow meter.

Background technology

For a long time, although orifice flowmeter and turbo flow meter have obtained using widely in natural gas flow measuring, there are some shortcomings in its inherent structure and principle, and littler than scope as the orifice flowmeter range, crushing is big, to the pulsating flow sensitivity; Though and turbo flow meter is compared the accuracy height with the former, range ratio is broad also, has movable member, the medium cleanliness is required high.Along with the growing interest of people, to the also raising thereupon of requirement of flowmeter to energy problem.Particularly the transmission of rock gas and metering are the major subjects that people are concerned about always, and how the accuracy of metering and the convenience of instrument installation and maintenance are taken into account then is the core of this problem.Along with the development of piezoelectric ceramic technology and high-speed figure treatment technology, late 1990s, ultrasonic gas flowmeter just enters measurement of gas flow scenes such as rock gas with its special advantages.

Compare with traditional flowmeter, ultrasonic flow meter has no movable member, and crushing is little, and accuracy of measurement is subjected to advantages such as medium temperature, pressure influence hardly, and especially aspect the large-caliber flow measurement, its superiority is more obvious.Over nearly 10 years, in engineering application and international trade, ultrasonic gas flowmeter has the trend of the traditional flow instrument of replacement of catching up from behind greatly.At present, surplus the U.S., Britain, Holland, Germany, Canada, the Russia etc. 10 national approved it be the measuring instrument of rock gas trade induction system.It is reported that China also carries out technological demonstration over against this, the formulation standard.Only the West-East National Gas Transmission Project with one of China four engineering of big century is an example, through flow metering demonstration repeatedly, with the first-selected instrument of ultrasonic gas flowmeter as natural gas flow measuring.

The signal detecting method that ultrasonic flow meter adopts has time difference method, phase difference method, frequency-difference method, Doppler method, correlation method, wave beam deflection method and noise method etc.Because the difference of speed reflected rate of flow of fluid when the ultimate principle of time difference method, phase difference method, frequency-difference method was all propagated by measurement ultrasonic signal following current and adverse current, so be referred to as the propagation speed differential method again, was the method that is most widely used at present.

Start from 20 years 20th century though adopt the ultrasound wave principle to measure flow, enter the practical stage seventies, and medium still is limited to liquid.The ultrasonic flow meter that is used for measurement gas results from the nineties, so far less than 20 years.Applications of ultrasound in the gas flow measurement is made slow progress, and main cause is that the specific acoustic impedance of gas and solid (material of ultrasonic transducer) is respectively 0.0004MRayl and 1～35MRayl (1MRayl=10 ⁶Ns/m ³), making that the sound transmission on gas and the solid interface is very low, the serious mismatch of this impedance has caused that gas ultrasonic transducer efficient is low, frequency band is narrow, the pulse remained shock is long.Add the hyperacoustic overdamp characteristic of gas medium-high frequency, the velocity of sound with environmental change, detect factors such as being subject to influence of environmental noise, make the gas ultrasonic testing system can't reach the sensitivity of general ultrasonic testing system, signal to noise ratio (S/N ratio) and resolution.

The error of propagation speed differential type ultrasonic flowmeter is mainly determined by the factor of two aspects: the one, and the precision of signal Processing, particularly ultrasonic signal decay bigger in gas, and it is bigger accurately to measure difficulty; The 2nd, fluid mechanic model that ultrasound wave transmits in the flow field is selected, and this is mainly reflected in sum of errors that the flow field velocity inequality causes the ultrasound wave ray tracing to change causing because flow field section velocity distribution inequality makes the different errors that cause of face average velocity of the line average velocity that records and reality.

Summary of the invention

Subject matter to be solved by this invention is the signal Processing precision not high problem of propagation speed differential type ultrasonic flowmeter in particular for the ultrasonic flow meter of gas flow detection.The present invention proposes following ultrasonic flow meter signal processing method for this reason, records rate of flow of fluid and flow thereby be used for measuring ultrasonic signal in the travel-time of measuring channel.

(1) utilize the coded modulation ultrasonic signal with autocorrelation characteristic, generation transmits;

(2) transmit to propagate and carried flow rate information through the pipeline flow field;

(3) receive and to have carried transmitting of flow rate information, and with step 1 in generate transmit and carry out related operation;

(4) accurately record travel-time of ultrasonic signal according to the peak of related function, calculate flow velocity and flow with this.

In the technique scheme, preferably select sign indicating number for use, as pseudo-random code etc. with good automatic correlative property as the coding of modulation.

The present invention has following outstanding advantage:

1. the coding relevant measurement method that proposes of the present invention existing difficulty of small mistiming of having avoided direct measurement receiving and transmitting signal can obtain the signal propagation time of high measurement accuracy;

2. classical correlative flow measuring method is based on the inner abiogenous random noise signal of convection cell and measures, and this noise comes from turbulent flow, and physical background is very complicated.And in the coding correlative flow measuring method that the present invention proposes, measurement to as if coded signal, as pseudo-random code, physical background is simply clear and definite, structure determines that by the primitive polynomial of selecting in advance is unique can repeat to produce, this has just got rid of the ambiguity of research object.

3. the relevant speed during the fluid velocity that the correlation technique of encoding records is measured than classical correlative flow has more clear physical meaning.If with certain or a few kinds of parameters of sensor sensing volume inner fluid in the related measuring system (as " vortex " in the single-phase flow, discrete phase concentration in the two-phase flow etc.) distribution or variation function definition are responsive, and what the relevant speed during then classical correlative flow is measured was represented is the flow rate information of this sensitivity field.Obviously, responsive is to become at random the time, so responsive randomness has determined the randomness of its representative flow velocity meaning, measured relevant speed is not to be the average velocity of fluid, so its physical significance waits clearly.And coding correlation technique essence still be the measuring ultrasonic wave flow principle, so the fluid velocity that records clearly is defined as the line average velocity on the sound path, is subjected to when converting fluid average velocity (face average velocity) to that the flow velocity profile is nemaline to be influenced.

4. the coding correlation technique has reduced source of error.According to classical correlative flow measure theory, related function integral time limited, upstream and downstream signalling channel (comprise sensor and corresponding demodulation, amplify and filtering circuit) characteristic matching degree all is the factor that causes measuring error.And in the coding correlation technique, because coded signal is periodically to determine signal as pseudo-random code, therefore the calculating of its related function can be finished in one-period, and does not have the requirement of endless integral time, and, system has only a signal circuit, does not therefore have the problem of channel matched.

Description of drawings

The frequency-difference method fluid-velocity survey schematic diagram of Fig. 1 propagation speed differential type ultrasonic flowmeter;

The classical correlative flow measuring principle of Fig. 2 figure;

Fig. 3 pseudo-random code autocorrelation function graph;

Coding correlative flow measuring process synoptic diagram in Fig. 4 ultrasonic flow meter of the present invention;

The related function shape synoptic diagram that Fig. 5 uses the pseudo-random code coding to obtain.

Embodiment

The present invention proposes a kind of ultrasonic flow meter signal processing method of novelty---coding measurement of correlation technology.Having of good autocorrelation performance coding important also is that comparison application early is range finding, no matter be traditional radar range finding or current state-of-the-art satellite navigation GPS (GPS), its travel-time measuring accuracy can reach the grade of approximate atomic clock.Thinking of the present invention derives from the above-mentioned fact.

It is as follows that the coding correlation technique is used for the principle of high-acruracy survey in ultrasonic gas flowmeter travel-time: according to correlation theory, and as Fig. 1, the transmit related function R of x (t) and downstream bb ' received signal y (t) of upstream aa ' _Xy(τ) the pairing time τ of peak ₀Be the transit time (travel-time of signal just).Therefore, the velocity of propagation v of signal x (t) in system _c(being commonly referred to relevant speed) can be by v _c=L/ τ ₀Calculate.Under desirable flow state, when just the speed of each point place fluid all equates on the cross-section of pipeline, the volume averaging flow velocity v of detected fluid _CpCan use relevant speed v _cRepresent that then the volume flow Q of detected fluid can be expressed as:

Q＝v _cp·A＝L/τ ₀·A

A is that pipeline section is long-pending in the formula

Some codings have the shape of similar δ function (impulse function) as the autocorrelation function of pseudo-random code (embodiments of the invention adopt m sequence), so its sharp-pointed peak feature has guaranteed the accuracy that the travel-time measures.Therefore, as long as the ultrasonic signal to emission carries out modulating-coding, as be modulated to pseudo-random code, the ultrasonic signal that receives is actual on time domain, have exactly one delay time transmit, both are made auto-correlation computation, the similar δ function of autocorrelation function shape then, corresponding time of its peak value is exactly above-mentioned time-delay, i.e. signal propagation time.

Modulating-coding thought is not limited to the m sequence in the pseudo-random code.The coding of using in the communications field is of a great variety, all can use so long as have the coding of good autocorrelation performance, as Gold sign indicating number, Barker code, quadratic residue sequence, Hall sequence, double-prime sequences etc.

Because the measuring accuracy of existing ultrasonic gas flowmeter is difficult to guarantee, considerable restraint is received in its application, method proposed by the invention is based on ultrasonic gas flow measurement achievement in research is proposed, but this method is not limited to gas flow measurement, in fact the ultrasonic decay in liquid of same frequency will be far smaller than gas, therefore the easier detection of ultrasonic signal in the liquid, precision is higher.

The present invention will be further described below in conjunction with drawings and Examples.

Measure at the correlative flow of encoding of the frequency-difference method ultrasonic flow meter in the propagation speed differential type.Frequency-difference method is the cycle frequency difference acquisition rate of flow of fluid of measuring following current and adverse current ultrasonic pulse, the method for flow value.The sound loop back path of ultrasonic gas flowmeter as shown in Figure 2, A and B are a pair of ultrasonic transducer, mutually alternately as transmitter and receiver.Its principle of work is: a transducer sends ultrasound wave, after another transducer receives ultrasonic signal, through triggering transmitter once more after certain signal Processing, form a sound cyclic process like this, this cycle frequency be cycle frequency when establishing following current the sound cycle frequency be f ₁, the sound cycle frequency is f during adverse current ₂, sound cycle frequency difference is Δ f.Ignore that ultrasound wave is propagated and electronic circuit equal time deferment factor in sensor, can get following formula and describe:

${\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="A20061001311300083.png,A20061001311300092.png"\; state="\{\{state\}\}">f</figure-callout>}}_1=\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A20061001311300083.png,A20061001311300092.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}=\frac{c+V\cos \mathrm{\&theta;}}{L}$

${\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="A20061001311300081.png,A20061001311300083.png"\; state="\{\{state\}\}">f</figure-callout>}}_2=\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20061001311300081.png,A20061001311300083.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}=\frac{c-V\cos \mathrm{\&theta;}}{L}$

$\mathrm{\&Delta;f}=f_1-{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="A20061001311300081.png,A20061001311300083.png"\; state="\{\{state\}\}">f</figure-callout>}}_2=\frac{2V\cos \mathrm{\&theta;}}{L}$

$V=\frac{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A20061001311300081.png,A20061001311300083.png"\; state="\{\{state\}\}">L</figure-callout>}}{2\cos \mathrm{\&theta;}}\mathrm{\&Delta;f}$

V-velocity of medium (m/s)

θ-ultrasonic propagation sound channel and tube hub wire clamp angle

The length (m) of L-ultrasound wave sound channel

t ₁-ultrasound wave following current the travel-time

t ₂-ultrasound wave adverse current the travel-time

As seen as long as accurately record the travel-time t of ultrasonic signal following current and adverse current ₁And t ₂, just can record rate of flow of fluid and flow.

Coding of the present invention uses the sign indicating number with good autocorrelation performance, a kind of as in the pseudo-random code---the m sequence.Produce by r level linear shift register, by 0 and 1 binary sequence that constitutes (not comprising complete 0 sequence), its longest possible cycle is p=2 ^r-1.Have the most macrocyclic this linear shift register sequence and be called maximum length linear shift register sequence or m sequence.

The m sequence has the random character of following three aspects:

(1) in each period p=2 ^rIn-1,0 occurs 2 ^R-1-1 time, and 1 appearance 2 ^R-1Inferior, i.e. 0 to 1 few appearance once;

(2) in each period p, have 2 ^R-1The distance of swimming of individual element (the element distance of swimming that is k is appearred being called a length in k element of the same race continuously).Wherein, length is that (ratio that the distance of swimming of 1≤k≤r-2) occurs is 2 to k ^-kIt is 1 distance of swimming and 0 distance of swimming that length is r-1 of r that a length is arranged at last;

The m sequence has the two level autocorrelation function characteristic, i.e. the shape of the similar impulse function of its autocorrelation function (δ function), and be periodic function, the cycle is p, as shown in Figure 3.

Coding correlative flow following current measuring process in the ultrasonic flow meter of the present invention can be illustrated with Fig. 4.Along two sections of conduit axis, be separately installed with two sonacs, according to fluid flow direction, the ultrasonic transducer emission ultrasonic (switching to accepting state during reverse-current metering) that install the upstream; The ultrasonic transducer that install in the downstream receives ultrasonic (switching to emission state during reverse-current metering).The system that two sensors, measuring channel and detected fluid of upstream and downstream are formed can be regarded as a signal system.

Among the present invention, utilize pseudo-random code m sequence modulation ultrasonic signal,, and, export signal x (t-τ)+n (t) of the fluid hydrodynamic noise n (t) that superposeed by conversion by the ultrasonic transducer reception in downstream.After the amplification of signal process, filtering, seizure synchronously and the demodulation of output, obtain the related function figure with pseudo random signal x (t) as related operation, as Fig. 5.The pairing time shifting t of this figure peak ₁=20.20 μ s are exactly the following current travel-time of ultrasonic signal in fluid.Related function is to calculate under the following conditions among the figure:

Caliber: 5mm

Installation form: 45 ° of Z-shaped installations

Medium: air

The velocity of sound: 340m/s

Flow velocity: 10m/s

Pseudo-random code: 1110100

Symbol width: 10 μ s

Peak value identification sample frequency: 100MHz

Measuring Time: 70 μ s

Travel-time t in the time of in like manner can trying to achieve the adverse current propagation ₂, try to achieve flow in view of the above.

Need to prove, here the detailed explanation that has been center deployment with embodiments of the invention, described optimal way or embodiment, should be understood to this instructions only is to describe invention by the mode that provides embodiment, in fact can change to some extent on some details of system's formation and use, these variations and application all should belong in the scope of the present invention.

Claims (2)

1, a kind of signal processing method of propagation speed differential type ultrasonic flowmeter is characterized in that, combines coding and classical correlative flow and measures, and step is as follows:

(1) utilize the coded modulation ultrasonic signal with autocorrelation characteristic, generation transmits;

(2) transmit to propagate and carried flow rate information through the pipeline flow field;

(3) receive and to have carried transmitting of flow rate information, and with step 1 in generate transmit and carry out related operation;

(4) accurately record travel-time of ultrasonic signal according to the peak of related function, calculate flow velocity and flow with this.

2, the signal processing method of propagation speed differential type ultrasonic flowmeter according to claim 1 is characterized in that, described have a kind of pseudo-random code of being encoded to of autocorrelation characteristic.

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