CN106643939A - Method for calculating ultrasonic transmission time through ultrasonic flowmeter - Google Patents

Abstract

The invention discloses a method for ultrasonic flowmeter to calculate ultrasonic propagation time. The maximum value x _max of the sampling value of the echo signal received by the ultrasonic transducer is used to find the highest peak w _h1 and calculate the number of times near the highest peak. The energy of the echo within a cycle, and then determine a threshold E _{th according to the calculated energy of several adjacent cycle echoes, and find the first wave whose energy exceeds the set threshold E th in} the echo signal as a reference Wave, to calculate the propagation time of the ultrasonic flowmeter, avoiding the error of looking for the reference wave, thus avoiding the error of one cycle or several cycles in the calculated propagation time, and this method improves the measurement accuracy of the propagation time.

Description

Method for Calculating Ultrasonic Propagation Time for Ultrasonic Flowmeter

technical field

The invention relates to the technical field of ultrasonic flow measurement, in particular to a method for ultrasonic flowmeters to calculate ultrasonic propagation time.

Background technique

The working principle of the time-difference method ultrasonic flowmeter is shown in Figure 1. It is measured based on the principle that there is a certain linear relationship between the medium flow rate and the time difference generated when the ultrasonic wave propagates forward and backward in the medium. As long as the time difference between forward and reverse flow is accurately measured, then The flow velocity and its linear relationship are obtained to obtain the flow velocity, and then the instantaneous flow and the cumulative flow can be obtained.

In Figure 1, S ₁ and S ₂ are two ultrasonic transducers respectively, V is the liquid flow rate, D is the pipe diameter, L is the sound path of the ultrasonic wave, and θ is the incident angle of the ultrasonic wave entering the liquid. _t1 is the propagation time _of the ultrasonic wave in the pipeline when the transducer S1 is transmitting and S2 is receiving, that is, the downstream time _{; t2} is the propagation time _of the ultrasonic wave in the pipeline when the transducer _S2 is transmitting and S1 is receiving, namely Backflow time.

The forward flow time t ₁ and the reverse flow time t ₂ of the ultrasonic flowmeter are respectively calculated by the following formulas, namely:

In the formula, C is the sound velocity of the ultrasonic signal in water, and ΔT is the time difference between forward and reverse flow, then:

Since the speed C of ultrasonic waves propagating in the fluid is much greater than the actual flow velocity V of the measured fluid, that is, C ² >>V ² , the formula (3) can be simplified as:

Here, the V measured by the ultrasonic flowmeter is the linear average flow velocity of the fluid along the sound channel, and the cross-sectional average flow velocity is needed for flow calculation, so we need to multiply the linear average velocity V by the fluid correction coefficient k and finally multiply by The instantaneous flow Q can be calculated by the cross-sectional area S of the pipeline. Its formula is as follows:

Q=S·kV=(πD ² /4)kV.

At present, the echo signal received by the ultrasonic transducer is generally sampled to obtain the sampling value of the entire echo waveform, as shown in Figure 2, in the echo signal, the Y axis is the signal amplitude, and the X axis is the signal coordinate . First find the maximum value x _max of the sampling value of the echo signal received by the ultrasonic transducer, and then according to the data obtained by the experiment, as shown in Figure 3, by analyzing the relationship between the flow change and the propagation time, it can be seen that in box 1 The point corresponding to w ₄ is the point corresponding to w 4, and the box 2 is the point corresponding to w ₅ , and the ratio between the peak value and the maximum value x _max is quite different, so a coefficient S set according to the maximum value x _max can be determined, and the coefficient The S value takes the average value of the two ratio values with the largest difference between the ratios of two adjacent echo wave peaks to the maximum value x _max , and the product of it and x _max is used as the threshold for finding the reference wave:

x _th = x _max × s

As shown in Figure 2, according to the threshold x _th , the first wave whose amplitude is greater than the threshold is found as the reference wave w _{reference wave} . Due to the influence of temperature, flow velocity, etc., the threshold x _th determined according to the experimental data does not satisfy Due to the requirements of the working conditions, the zero-crossing point calculated by linear interpolation based on the reference wave found by the threshold x _th may have an error of one cycle or several cycles, which eventually leads to an error of one cycle or several cycles in the calculated propagation time.

Contents of the invention

The purpose of the present invention is to provide a method for ultrasonic flowmeter to calculate ultrasonic propagation time, which improves the accuracy of ultrasonic flowmeter propagation time measurement and reduces measurement errors.

The purpose of the present invention is achieved by adopting the following scheme: a method for ultrasonic flowmeter to calculate ultrasonic propagation time, the ultrasonic transducer transmitting end transmits ultrasonic signal, the ultrasonic transducer receiving end receives ultrasonic echo signal, and the ultrasonic wave propagates The calculation method of time includes the following steps:

1) Find the maximum echo amplitude point in the echo signal sampling value received by the receiving end of the ultrasonic transducer;

2) Calculate the energy of the echo within the period where the maximum point of the echo amplitude is located and the energy of the echo within several periods close to the period where the point of the maximum amplitude of the echo is located, and determine the maximum echo energy value E _max ;

3) The threshold value E _th is obtained according to the formula E _th =E _max ×S _E , wherein the value of the coefficient S _E is the average value of the two ratio values with the largest difference between two adjacent echo energy values and the maximum value E _max . The value of the coefficient S _E is taken between 0-1.

4) Find the echo in the period corresponding to the first echo energy greater than the threshold E _th according to the order of the echo cycle as the reference wave w _{reference wave} , and calculate the time t0 of the _zero -crossing point of the reference wave w _{reference wave} , according to the formula T=t ₀ +t', the ultrasonic propagation time T can be obtained. In the formula, t' is a fixed value related to the ultrasonic flowmeter.

The energy of the echo in each period is the sum of the amplitudes of all sampling points in the period.

In the reference wave w _{reference wave} , if the amplitude and polarity of two adjacent sampling points are opposite, the linear interpolation operation is performed to calculate the signal zero-crossing time t ₀ of the reference wave w _{reference wave} .

Calculate t' in the case of zero flow: when the fluid in the pipeline of the ultrasonic flowmeter is still, the accurate propagation time T ₀ at this time is calculated by measuring the length of the sound channel and according to the sound velocity at this time, and at the same time calculate the time at zero flow rate The time t' ₀ corresponding to the zero crossing point, then t'=t' ₀ -T ₀ .

Compare the energy of the echoes in each cycle calculated in step 2) with the threshold value E _th obtained in step 3) according to the cycle order, and use the echo in the cycle corresponding to the first echo energy greater than the threshold value as a reference Wave w _{reference wave} .

Step 2) Calculate the energy of the echo in the period where the maximum point of the echo amplitude is located and the echoes in two or three adjacent periods that are similar to the period of the maximum point of the echo amplitude energy, determine the maximum echo energy E _max .

The present invention has the advantages that: the method finds the highest peak w _h1 through the maximum value x _max of the sampling value of the echo signal received by the ultrasonic transducer, calculates the energy of the echo within several cycles near the highest peak, and then A threshold is determined according to the energy of several adjacent cycles of echoes obtained. The present invention uses the energy of the echoes to set the threshold E _th , and finds the first echo signal whose energy exceeds the set threshold E _th . The wave is used as the reference wave for calculating the zero-crossing time to calculate the propagation time of the ultrasonic flowmeter. Compared with the threshold value x _th set by the maximum value x _max of the sampling value of the echo signal to determine the reference wave, it avoids the ultrasonic flowmeter due to When the flow rate changes, the amplitude of the echo signal changes, which causes an error of one cycle or several cycles in the reference wave determined according to the threshold x _th , resulting in an error of one cycle or several cycles in the calculated propagation time. This method Improved accuracy of propagation time measurements.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the transit-time method super flowmeter;

FIG. 2 is a schematic diagram of an echo signal;

Figure 3 is a ratio diagram of the peak value and the maximum value x _max under different flow rates;

Fig. 4 is a schematic diagram of an echo signal and its echo energy;

Fig. 5 is a schematic diagram of the principle of calculating the zero-crossing point t ₀ by linear interpolation.

detailed description

In order to make the purpose, technical scheme and advantages of the present invention clearer, detailed implementation and specific operation process are provided, and the present invention will be further described in detail below in conjunction with the accompanying drawings:

Referring to Figure 4 and Figure 5, a method for calculating ultrasonic propagation time for an ultrasonic flowmeter, the transmitting end of the ultrasonic transducer transmits an ultrasonic signal, and the receiving end of the ultrasonic transducer receives an ultrasonic echo signal, and the calculation method for ultrasonic propagation time includes the following step:

1) find the echo amplitude maximum point x _max in the echo signal sampling value received by the receiving end of the ultrasonic transducer;

2) Respectively calculate the energy of the echo w _h1 in the cycle where the maximum echo amplitude point x _max is located and the echo energy in several cycles close to the cycle where the maximum echo amplitude point is located, and determine The echo energy maximum value E _max among the echoes in the above period. The present invention generally obtains the energy of the echoes in multiple adjacent periods including the echo w _h1 respectively. Preferably, the present invention separately obtains the energy of the echo in the period where the echo amplitude maximum point is located and the energy in two or three adjacent periods that are close to the period where the echo amplitude maximum point is located. The energy of the echo, determine the maximum echo energy E _max . As in this embodiment, the energies E ₁ , E ₂ , E _h1 , E of the echoes w ₁ , w ₂ , w _h1 , w ₄ , and w ₅ in five adjacent periods including the echo w _h1 are calculated respectively. ₄ , E ₅ . Wherein, E ₄ is the maximum echo energy E _max among the echoes in five adjacent periods. The energy of the echo in each period is the sum of the amplitudes of all sampling points in the period. For example, the echo energy E _i is calculated by the following formula: E _i = x _i + x _i+1 +…+ x _i+n , where i is the coordinate starting point of the echo w _i , and n is the sampling period of the echo The number of points, x _i is the echo amplitude. The echoes w ₁ , w ₂ are located before the echo w _h1 , and the echoes w ₄ , w ₅ are located behind the echo w _h1 .

3) The threshold value E _th is obtained according to the formula E _th =E _max ×S _E , wherein the value of the coefficient S _E is the average value of the two ratio values with the largest difference between two adjacent echo energy values and the maximum value E _max . In this embodiment, the difference between E ₁ /E _max and E ₂ /E _max , the difference between E ₂ /E _max and E _h1 /E _max , the difference between E _h1 /E _max and E ₄ /E _max , the difference between E ₄ /E _max and E ₅ /E _max , and it is obtained that the difference between E ₄ /E _max and E ₅ /E _max is the largest among the four differences, then the value of coefficient S _E is E ₄ /E _max and E ₅ / Mean value of _Emax . The value of the coefficient S _E is taken between 0-1. The threshold E _th in this embodiment is greater than the energy E ₁ , the energy E ₂ , and the energy E ₅ , and smaller than the energy E _h1 and the energy E ₄ .

4) Find the echo in the period corresponding to the first echo energy greater than the threshold E _th in order of period as the reference wave w _{reference wave} , the reference wave w _{reference wave} is the first wave whose energy is greater than the threshold. In this embodiment, the echo w _h1 is the first wave whose energy is greater than the threshold. Therefore, the w _{reference wave} in this embodiment is the echo w _h1 . Then the time t ₀ of the zero-crossing point of the reference _wave w is calculated, and the ultrasonic propagation time T can be obtained according to the formula T=t ₀ +t', where t' is a fixed value. In the reference wave w _{reference wave} , if the amplitude x _n of the nth point is opposite in polarity to the amplitude x _n+1 of the n+1th point, that is, when the amplitudes of two adjacent sampling points are opposite in polarity, linear interpolation is performed Calculate the signal zero-crossing time t ₀ of the reference wave w _{reference wave} . Take the calculated echo signal coordinate x _{zero-crossing point} as the signal zero-crossing time t ₀ , as shown in Figure 5, the zero-crossing time t ₀ calculated by linear interpolation:

In this embodiment, the energy of the echoes in each cycle calculated in step 2) is compared with the threshold value _Eth obtained in step 3) according to the cycle order, and the energy in the cycle corresponding to the first echo energy greater than the threshold value The echo serves as the reference wave w _{reference wave} .

Calculate t' in the case of zero flow: when the fluid in the pipeline of the ultrasonic flowmeter is still, the accurate propagation time T ₀ at this time is calculated by measuring the length of the sound channel and according to the sound velocity at this time, and at the same time calculate the time at zero flow rate The time t' ₀ corresponding to the zero crossing point, then t'=t' ₀ -T ₀ .

The forward flow time t ₁ and the reverse flow time t ₂ calculated by the above method in the present invention have high accuracy and can meet the measurement requirements of the ultrasonic flowmeter.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (6)

1. it is a kind of for ultrasonic flowmeter calculate ultrasonic propagation time method, it is characterised in that ultrasonic transducer send out End transmitting ultrasonic signal is penetrated, ultrasonic transducer receiving terminal receives ultrasound echo signal, the calculating side of ultrasonic propagation time Method comprises the steps：

1) the echo amplitude maximum point in the echo signal sample value that ultrasonic transducer receiving terminal is received is found；

2) ask for respectively echo in the cycle residing for echo amplitude maximum point energy and with the echo amplitude maximum point institute The energy of the echo in close several cycles place's cycle, determines backward energy maximum E_max；

3) according to formula E_th=E_max×S_EObtain threshold value E_th, wherein, coefficient S_EValue takes two neighboring backward energy value and maximum E_maxMaximum two ratio values of ratio difference mean value；

4) according to echo cycle sequences first is found more than threshold value E_thBackward energy corresponding to cycle in echo conduct Reference wave w_{Reference wave}, calculate reference wave w_{Reference wave}Zero crossing time t₀, according to formula T=t₀+ t' can obtain ultrasonic wave Propagation time T, in formula, t' is a fixed value related to ultrasonic flowmeter.

2. method according to claim 1, it is characterised in that：The energy of the echo in each cycle is the institute in the cycle The summation that the amplitude for having sampled point is added.

3. method according to claim 1, it is characterised in that：In reference wave w_{Reference wave}In, if the width of adjacent two sampled point Linear interpolation arithmetic is then carried out during value opposite polarity, reference wave w is calculated_{Reference wave}Signal zero-crossing time t₀。

4. the method according to claim 1 or 3, it is characterised in that：T' is calculated in the case of zero delivery：Work as supersonic flow Now accurately passed by measuring the length and calculating according to the velocity of sound now of sound channel when fluid in gauge pipeline is static T between sowing time₀, while calculating the corresponding time t' of zero crossing under zero flow velocity₀, then t'=t'₀-T₀。

5. method according to claim 1, it is characterised in that：By step 2) echo in each cycle for calculating Energy is according to cycle sequences and step 3) threshold value E that obtains_thIt is compared, by corresponding to first backward energy more than threshold value Cycle in echo as reference wave w_{Reference wave}。

6. method according to claim 1, it is characterised in that：Step 2) week residing for the echo amplitude maximum point is asked for respectively The energy of the echo in the phase and in front and back each two or three adjacent periods close with the cycle residing for echo amplitude maximum point The energy of interior echo, determines backward energy maximum E_max。