Voltage difference ultrasonic flow detection method

Abstract

The application discloses a voltage difference ultrasonic flow detection method, and belongs to the technical field of ultrasonic flow detection. In order to solve the problems of high cost and poor measurement accuracy of the time difference method ultrasonic flow detection method in the small pipeline small flow scene, two ultrasonic signals propagating along the same propagation time path are introduced to the piezoelectric ceramic along the forward flow and the reverse flow, at this time, the piezoelectric ceramic enters a special positive piezoelectric effect state, the piezoelectric ceramic generates a corresponding receiving voltage, and the receiving voltage amplitude will change according to the flow size. According to the positive piezoelectric effect, the process is deduced, and the measurement method and the analytical formula under different working modes are obtained. The voltage measurement circuit is used to measure the voltage size, and the analytical formula of the corresponding working mode is selected to directly deduce and obtain the actual flow size. The application is used for ultrasonic-based flow detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ultrasonic flow detection, and relates to an ultrasonic-based flow detection method. BACKGROUND

[0002] In recent decades, ultrasonic flow measurement technology has been considered as an important solution for flow detection in the fields of chemistry, medicine and industry. This is mainly due to the fact that ultrasonic waves do not interfere with the fluid during the measurement process, while having the advantages of high sensitivity and low cost. According to the different measurement methods, ultrasonic flow measurement technology can be divided into three types: time difference method, Doppler method and phase method. Among them, the time difference method is a widely used method, and it has various installation methods. Compared with the Doppler method and the phase method, the time difference method can be applied to more scenarios. When measuring the flow by using the time difference method, there are various installation methods for ultrasonic transducers, such as plug-in type, pipe segment type and external clamping type. The measurement principles of different installation methods of the time difference method are similar. Taking a pair of external clamping transducers as an example, the main measurement principle of the time difference method is shown in FIG. 1. Figure 1

[0003] The transducers are arranged at the upstream and downstream ends of the pipeline, respectively. First, a transducer transmits a series of ultrasonic waves to another transducer, for example, from the upstream to the downstream. At this time, the upstream transducer acts as the transmitting end, and the downstream transducer acts as the receiving end. The ultrasonic waves propagate downstream in the fluid, as shown by the white line in the figure. Since the fluid direction is the same as the ultrasonic wave propagation direction, the arrival time of the ultrasonic wave is earlier than that without flow. Conversely, the downstream transducer transmits ultrasonic waves to the upstream transducer. At this time, the downstream transducer acts as the transmitting end, and the upstream transducer acts as the receiving end. The ultrasonic waves propagate upstream in the fluid, as shown by the red line in the figure. Since the fluid direction is opposite to the ultrasonic wave propagation direction, the ultrasonic wave propagation time becomes longer, and the arrival time is delayed compared to the case without flow. In this way, the time difference between the two transmitted ultrasonic wave signals is generated. The actual flow size can be calculated by using the time difference. The flow measurement formula is shown as follows:

[0004]

[0005] In the formula, Q is the flow size; K x is the correction coefficient; n is related to the Reynolds number Re, and is a constant for a certain flow rate of liquid; k is the number of straight-line propagation of ultrasonic waves in the liquid; R is the radius of the pipeline; c l is the ultrasonic wave speed in the liquid; and φ is the angle between the ultrasonic wave trajectory on the liquid side and the interface.

[0006] The relationship between the Reynolds number Re and n is shown in the following table:

[0007] Table 1 Relationship between Reynolds number Re and n ​

[0008]

[0009] For the determination of the Reynolds number of the liquid flowing in the pipeline, there is a formula:

[0010]

[0011] In the formula, p is the density of the liquid (kg / m 3 ); μ is the dynamic viscosity coefficient of the liquid (mPa·s).

[0012] The time difference flow detection method has obvious advantages, but it also has some disadvantages. In the time difference flow measurement, the transducer usually works in a transmit-receive mode. To realize the switching of the forward and reverse propagation directions of the ultrasonic waves, the transmitting and receiving functions of the transducer need to be switched, which is mainly completed through the transmitting and receiving circuits connected to the transducer. In actual application, it is inevitable to measure the forward and reverse signal data of the ultrasonic waves continuously twice in adjacent time. When measuring the flow by the time difference method, the forward and reverse ultrasonic signals required are collected at different times, which introduces errors. At the same time, the time difference method relies too much on the signal collection ability of the equipment. The higher the collection speed, the smaller the time step of the collected data, and the more accurate the ultrasonic time difference calculated from the collected data, but the amount of collected data will also increase, resulting in slower calculation speed and further amplification of the influence of time-sharing measurement. In addition, in the measurement scene of small pipeline and small flow, the time difference generated by small flow is often less than 1 ns. If the measurement accuracy is still less than ±1% at this time, the time measurement accuracy needs to be less than ±1% of the time difference, that is, ±10 ps. Obviously, such measurement accuracy will greatly increase the cost of the measurement equipment. Even if the time measurement accuracy of the equipment is high enough, the time difference method will still have poor small flow measurement effect due to the flow fluctuation problem of time-sharing measurement, and the general error is far more than ±10%. Therefore, the existing ultrasonic flowmeter products will not choose to publicize the measurement error percentage of the equipment at small flow when they are promoted, but choose to publicize the resolution of the actual flow speed, such as the minimum flow speed resolution ±0.01 m / s. SUMMARY

[0013] The present application solves the problem of high cost and poor measurement accuracy of the time difference method ultrasonic flow detection method in the small pipeline and small flow scene.

[0014] A voltage difference ultrasonic flow detection method, based on transducer detection of fluid, using a piezoelectric ceramic to simultaneously receive two ultrasonic signals of forward and reverse flow, based on the collected voltage signals V end and V max , the flow is obtained according to the first measurement formula:

[0015] The first measurement formula is:

[0016]

[0017] In the formula, Q is the flow size; K x is the correction coefficient; k is the number of straight-line propagation of ultrasonic waves in the liquid, and the "V" shape reflection in the pipeline is counted as two straight-line propagation; R is the pipeline radius; c l is the ultrasonic wave speed in the liquid; φ is the angle between the liquid-side ultrasonic wave trajectory and the interface corresponding to the interface between the pipeline wall and the liquid; ω is the piezoelectric ceramic resonance frequency; V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0018] Further, the correction coefficient n is a constant related to the Reynolds number Re.

[0019] Further, the first measurement formula is determined by the following process:

[0020] According to the characteristics of Fourier decomposition, the displacement solving equation when the piezoelectric ceramic vibrates is determined, and based on the steady-state response, the piezoelectric ceramic vibration is simplified as

[0021]

[0022] In the formula, m is the mass of the piezoelectric ceramic; c is the damping coefficient; k is the stiffness; x(t) is the displacement of the piezoelectric ceramic, t is the time; i is the imaginary unit, and A represents the amplitude of the sine wave; ω is the natural resonance frequency of the piezoelectric ceramic;

[0023] The equation is solved to obtain the forced vibration response as follows:

[0024] x(t) = S1exp((-ξ1+ξ2)t) + S2exp((-ξ1-ξ2)t) +

[0025] (X2+iX1)exp(-iωt) + (X2-iX1)exp(iωt)

[0026] The forward flow and reverse flow signals are respectively denoted as x(t+Δt) and x(t-Δt), and a piezoelectric ceramic is used to simultaneously receive the two ultrasonic signals of the forward flow and the reverse flow, and the two ultrasonic signals are considered to be taken in the resultant direction, that is, directly added

[0027]

[0028] In the voltage steady-state response, there is:

[0029] V(t) = V x ·x(t)

[0030]

[0031] In the formula, V(t) is a function of the voltage steady-state response, V x is a coefficient; V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0032] A voltage difference ultrasonic flow detection method, for the case that the transmitting signal of a transducer is not adjustable, based on the detection of the transducer on fluid, using a piezoelectric ceramic to simultaneously receive two ultrasonic signals of forward flow and reverse flow, measuring the amplitudes M and N of the two received signals, obtaining K=N / M and the time delay Δt that the two ultrasonic waves cannot completely arrive at m ; according to V end , V max , K, Δt m , using a second measurement formula to obtain the flow;

[0033] Second measurement formula:

[0034]

[0035] In the formula, Q is the flow size; K x is a correction coefficient; k is the number of straight-line transmissions of ultrasonic waves in liquid, and one "V" shaped reflection in the pipeline is recorded as two straight-line transmissions; R is the pipeline radius; c l is the ultrasonic wave speed in liquid; φ is the angle between the liquid side ultrasonic wave trajectory corresponding to the interface between the pipeline wall and liquid and the interface; ω is the piezoelectric ceramic resonance frequency; V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0036] Further, the correction coefficient n is a constant related to the Reynolds number Re.

[0037] Further, the first measurement formula is determined by the following process:

[0038] First, the first measurement formula is determined:

[0039]

[0040] When the transmitting time is not adjustable, the two ultrasonic waves transmitted simultaneously cannot completely arrive at the same time, resulting in a time delay Δt m , and the formula compensation is

[0041]

[0042] For the two receiving signal amplitude non-adjustable case of forward and reverse flow, let the current signal be M x (t-Δt) and N x (t+Δt), M and N represent the respective amplitude, the new superimposed signal is:

[0043]

[0044] K=N / M

[0045] By determining K, continue to measure the flow by voltage difference; and determine the second measurement formula

[0046]

[0047] Where, V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0048] A voltage difference ultrasonic flow detection method, for the adjustable case of the transmitting signal of the transducer, based on the transducer for detecting fluid, using a piezoelectric ceramic to receive two ultrasonic signals of forward and reverse flow, the detection includes the following steps:

[0049] (1) The two transmitting signals are received by the receiving piezoelectric ceramic, the amplitude relationship of the two receiving signals is observed, the amplitude of the excitation signal is adjusted and retransmitted; the two receiving signals are adjusted to the same amplitude;

[0050] (2) Adjust the delay time so that the two receiving signals can reach the piezoelectric ceramic at the same time under no flow condition in the pipeline;

[0051] (3) Based on the previous two steps, adjust the excitation signal to eliminate the amplitude difference and time difference of the two ultrasonic waves; when measuring the flow, the first measurement formula is used for flow measurement, and the first measurement flow is obtained;

[0052] The first measurement formula is:

[0053]

[0054] In the formula, Q is the flow size; K x is the correction coefficient; k is the number of straight-line propagation of ultrasonic waves in liquid, and one "V" shaped reflection in the pipeline is counted as two straight-line propagation; R is the radius of the pipeline; c l is the ultrasonic wave speed in liquid; φ is the angle between the liquid side ultrasonic wave trajectory and the interface corresponding to the pipe wall and liquid; ω is the piezoelectric ceramic resonance frequency; V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0055] According to obtain the signal time difference Δt generated by the flow;

[0056] (4) based on the time difference Δt, using calculate the artificial delay t delay , t delay as the excitation signal delay to re-excite the piezoelectric ceramic, so that the two ultrasonic signals are as follows:

[0057] V + (t) = V(t + t delay )

[0058] V - (t) = V(t - t delay )

[0059] re-measure the voltage V start and V end size;

[0060] (5) according to the third measurement formula to obtain the final flow;

[0061] Third measurement formula:

[0062]

[0063] where θ is an intermediate variable,

[0064] Further, in step (4), when re-measuring the voltage V start and V end size, V start is indirectly measured by V start = cos(ωt delay )·V max .

[0065] Further, the correction coefficient n is a constant related to the Reynolds number Re.

[0066] Further, the third measurement formula is determined by the following process:

[0067] First, determine the first measurement formula:

[0068]

[0069] In the process of determining the first measurement formula, it is obtained that

[0070]

[0071] Further, it is determined that the relationship between the time difference and the voltage difference presents a nonlinear relationship;

[0072] The delay of the ultrasonic excitation signal is adjusted based on the artificial delay t. delay The voltage signal obtained is as follows:

[0073] V + (t)=V(t+t delay )

[0074] V - (t)=V(tt delay )

[0075] When there is no flow in the pipe, the two signals will be superimposed without being affected by the flow rate:

[0076] V start =V + (t)+V - (t)=V x ·2cos(ωt delay x(t)

[0077] In the formula, V start It presets the initial voltage amplitude under no flow after a delay;

[0078] The artificially delayed signal experiences a time difference due to the flow rate. The magnitude of the superimposed signal voltage V at this point, when there is flow, is... end Become

[0079] V end =V + (t+Δt)+V - (t-Δt)=V x ·2cos(ω(t delay +Δt))x(t)

[0080] The results show that the voltage difference in the signal caused by the flow rate is a function of the artificial delay. Taking the derivative with respect to the delay time to obtain the maximum value of the function yields...

[0081]

[0082] The output voltage difference reaches its maximum value.

[0083] ΔV=V x ·X3(cos(nπ)-cos((-1) n+1 nπ-ωΔt)

[0084] With the initial transmission delay of the transducer adjustable, the adjustment of the above formula ensures that the voltage difference generated each time is the maximum voltage difference that the measuring device can generate under the current flow rate; thus, the third measurement formula is determined.

[0085]

[0086] where θ is an intermediate variable determined by and together determine a unique value.

[0087] Advantages of the present application:

[0088] 1. Using a piezoelectric ceramic to receive two ultrasonic signals at the same time, the time difference information of the two signals will be converted into voltage difference information. Voltage difference method is suitable for a wide range of flow detection scenarios, whether it is a pipe section, plug-in or external clamping ultrasonic flowmeter can use this measurement method. Because the voltage measurement device has low cost and high measurement accuracy, the voltage difference ultrasonic flow detection method is a high-precision and low-cost ultrasonic flow detection method.

[0089] 2. According to the actual use requirements and different scenes, the voltage difference flow detection method is discussed in detail, and the method for improving the accuracy of the voltage difference flow detection method is given. In the high degree of freedom adjustment mode, the use of voltage difference method to measure the flow can greatly increase the measurement voltage difference and improve the measurement accuracy. Even in the case of no adjustment, the measurement process can be corrected by determining the signal amplitude and arrival time information to improve the measurement accuracy. The signal enhancement and influence factor elimination method expands the application scene and scope of the voltage difference flow detection method, and has strong universality. BRIEF DESCRIPTION OF DRAWINGS

[0090] Figure 1 Time difference flow measurement principle diagram for external clamping transducer.

[0091] Figure 2 Piezoelectric ceramic vibration response diagram.

[0092] Figure 3 Piezoelectric ceramic single-sided receiving / transmitting ultrasonic signal.

[0093] Figure 4 Piezoelectric ceramic double-sided simultaneous receiving / transmitting ultrasonic signal.

[0094] Figure 5 Time difference to voltage difference diagram.

[0095] Figure 6 Voltage difference flow detection transducer arrangement example.

[0096] Figure 7 Voltage difference amplitude size relationship.

[0097] Figure 8 Voltage difference flow measurement result diagram. DETAILED DESCRIPTION

[0098] The present application aims to solve the problem of high cost and poor measurement accuracy of time difference method ultrasonic flow detection method in small pipeline and small flow scene, and proposes a method for measuring flow by measuring voltage difference, and according to different measurement scenes, the method is improved to solve various actual measurement problems. The method can be applied to various ultrasonic flow detection scenes such as external clamping, pipe section and invasion.

[0099] The method introduces two ultrasonic signals propagating along the same path in the same direction and in the opposite direction to the piezoelectric ceramic according to the propagation time, at this time the piezoelectric ceramic enters a special positive piezoelectric effect state, and the piezoelectric ceramic generates a corresponding receiving voltage, the amplitude of the receiving voltage will change according to the flow size. According to the positive piezoelectric effect, the process is deduced and the measurement method and analytical formula under different working modes are obtained. The voltage measurement circuit is used to measure the voltage size, and the analytical formula of the corresponding working mode can be directly deduced to obtain the actual flow size. The measurement accuracy of the voltage difference method is compared with that of the time difference method, and the voltage difference method can have better measurement accuracy in the case of small time difference. At the same time, even if the voltage measurement circuit is of super-high precision, the hardware cost is much lower than that of the high-precision time measurement device. After the voltage measurement is completed, the voltage difference ultrasonic flow measurement method does not need complex algorithm processing, and the calculation amount is much smaller than that of the time difference method which generally uses cross-correlation algorithm. Since the two-way signal is transmitted at the same time, the disadvantage of time-sharing measurement is eliminated. The advantages of the voltage difference method can greatly speed up the single flow detection speed, thereby improving the measurement accuracy.

[0100] The method of the present application utilizes the positive piezoelectric effect of ultrasonic waves on piezoelectric ceramics to superimpose two ultrasonic waves propagating along the same length and having high similarity in the same direction and in the opposite direction. By further analyzing the superimposed signal, the flow measurement formula under different conditions is derived for different transmission signals, and then ultrasonic flow detection is realized. The present application will be further described in conjunction with the specific embodiments. Specific embodiment one:

[0102] The present embodiment is a voltage difference ultrasonic flow detection method, and the specific implementation process is as follows:

[0103] First of all, two transmission transducers need to be able to generate stable ultrasonic signals. Generally speaking, when a transducer is applied with a stable frequency signal (the signal has a determined stable frequency peak in the frequency domain, and the frequency corresponding to the peak is the resonant frequency of the piezoelectric ceramic), its vibration response is as shown in Figure 2 .

[0104] The ultrasonic signal generated by piezoelectric ceramics can be divided into two processes: forced vibration (including transient response and steady-state response) and free vibration. Since the amplitude of the free vibration stage is small and uncontrollable, the method mainly utilizes the steady-state response in the forced vibration process of piezoelectric ceramics.

[0105] According to the characteristics of Fourier decomposition, when the square wave, sine wave, triangle wave, sawtooth wave and other signals with a certain frequency are transformed from time domain to frequency domain, a maximum point will appear at the above-mentioned certain frequency in the frequency domain signal. This means that the frequency has the largest proportion of all signal frequencies, and other frequency components have a small proportion and can be ignored. When the signal is converted back from the frequency domain to the time domain, the time domain signal is a sine wave after ignoring other frequency components. The displacement equation of piezoelectric ceramic vibration is as follows:

[0106]

[0107] In the formula, m is the mass of the piezoelectric ceramic; c is the damping coefficient; k is the stiffness; x(t) is the displacement of the piezoelectric ceramic, where t is the time; A(exp(-iωt)-exp(iωt))i is the sine excitation signal, i is the imaginary unit, A represents the amplitude of the sine wave; ω is the natural resonant frequency of the piezoelectric ceramic; is the first derivative of displacement with respect to time, i.e. velocity; is the second derivative of displacement with respect to time, i.e. acceleration.

[0108] Solving the equation, the forced vibration response thereof is as follows:

[0109]

[0110] wherein

[0111]

[0112] ξ1=-(λ1+λ2) / 2=c / 2m

[0113] ξ2=λ1-λ2

[0114] S1=2(λ2X2-ωX1) / (λ1-λ2)

[0115] S2=-(λ1S1+ωX) / λ2

[0116]

[0117] In the forced vibration solution, S1exp((-ξ1+ξ2)t)+S2exp((-ξ1-ξ2)t) is the transient response part, and (X2+iX1)exp(-iωt)+(X2-iX1)exp(iωt) is the steady-state response part. When only considering the steady-state response, the piezoelectric ceramic vibration solution can be simplified as

[0118]

[0119] According to the background art, the upflow and downflow ultrasonic wave propagation time generated by the two transmitting transducers synchronously increases and decreases, and thus it is assumed that the upflow and downflow signals generated by the two transmitting transducers are x(t+Δt) and x(t-Δt), respectively.

[0120] As shown in Figure 3 , whether the received piezoelectric ceramic is receiving ultrasonic waves on the same side or on both sides, the two ultrasonic signals can be considered to be in the resultant direction, i.e., directly added

[0121]

[0122] At this time, the relationship between the ultrasonic signal and the time difference when there is no flow and when there is flow is clear, and the flow detection formula under different conditions can be derived according to formula (5). Since the received ultrasonic signal is an electrical signal rather than an actual displacement during detection, the process is the process of generating an electrical signal by the piezoelectric ceramic subjected to vibration, which is consistent with the principle of being subjected to an electrical signal vibration. At this time, the displacement signal is used as an excitation, and the solution is a voltage signal. Therefore, when only considering the steady-state displacement signal as an excitation, the displacement is in a sinusoidal form, and thus the voltage solution must contain the transient response and the steady-state response of the voltage. The voltage steady-state response is a function linearly related to the displacement steady-state response, and the coefficient is V x . Therefore, when considering the voltage steady-state response, formula (5) can be further rewritten as

[0123] V(t)=V x ·x(t)

[0124]

[0125] In the formula, V(t) is a function of the voltage steady-state response; V end is the voltage amplitude of the superimposed signal when there is flow; and V max is the voltage amplitude of the superimposed signal when there is no flow.

[0126] Under ideal conditions, the received upflow and downflow ultrasonic signals should be ultrasonic signals with consistent amplitudes, as shown in the above assumption. However, in fact, according to different measurement methods, the ultrasonic signal amplitude is sometimes not adjustable, such as Figure 4The two sides of the ultrasonic signal are generated at the same time, and the transmission time and amplitude of a single signal cannot be controlled, which is a form of piezoelectric ceramic two-sided simultaneous reception / transmission of ultrasonic signals. Figure 3 The measurement method shown not only has adjustable amplitude, but also has adjustable transmission time on the left and right sides, which is a form of piezoelectric ceramic single-sided reception / transmission of ultrasonic signals. For different types of measurement methods, they can be mainly classified as: 1) The measurement scene is simple, and certain errors can be tolerated, that is, the measurement scene is considered ideal, the calculation amount is the smallest, and the measurement accuracy is general. 2) The amplitude and transmission delay cannot be adjusted, but the influence of the amplitude on the measurement needs to be considered, the calculation amount is general, and the measurement precision is better. 3) The amplitude and transmission delay can be adjusted, which can improve the measurement sensitivity, the calculation amount is the largest, and the measurement precision is the best.

[0127] Figure 5 The measured signals of two ultrasonic signals with the same amplitude and no time difference and the time difference that can completely cancel the steady-state response are shown.

[0128] 1) Voltage difference method flow measurement formula in ideal case:

[0129] The voltage difference method flow measurement formula in ideal case can be used as a simplified formula in special cases. In the ideal case, the formula has the simplest form and is easier to calculate. Directly substitute formula (6) into the flow measurement formula in the background technology, and the voltage difference method flow measurement formula in the ideal case is as follows:

[0130]

[0131] In the formula, Q is the flow size; K x is the correction coefficient; n is a constant related to the Reynolds number Re; k is the number of straight-line propagation of ultrasonic waves in the liquid, such as Figure 4 the "V" shape reflection in the pipeline is recorded as 2 times of straight-line propagation; R is the radius of the pipeline; c l is the ultrasonic wave speed in the liquid; φ is the angle between the liquid-side ultrasonic wave trajectory and the interface with the liquid as the interface; ω is the piezoelectric ceramic resonance frequency. V end is the superimposed signal voltage amplitude size when there is flow; V max is the superimposed signal voltage amplitude size when there is no flow.

[0132] 2) Voltage difference method flow measurement formula when the transmission signal is not adjustable:

[0133] In special cases, the transmission time and amplitude of the two ultrasonic signals cannot be adjusted independently according to the set parameters.

[0134] When the transmission time is not adjustable, it is usually shown that the two ultrasonic waves cannot reach at the same time completely, which is mainly caused by the slight asymmetry of the propagation path and the circuit delay. Although this part of the time difference cannot be compensated by adjustment, its actual value can be obtained by measurement, and the actual value can be used to compensate the measurement. Assuming that a time difference Δt m is generated due to the above reasons

[0135]

[0136] For the amplitude of the two received signals of the forward and reverse flow, the amplitude is not adjustable. Assuming that the current signal is Mx(t-Δt) and Nx(t+Δt), M and N represent the amplitudes of the corresponding signals respectively, the new superimposed signal can be obtained as follows:

[0137]

[0138] By determining K, the flow measurement can be continued by the voltage difference. Considering the voltage difference flow measurement formula when the parameters are not adjustable but can be determined:

[0139]

[0140] Where, V end is the amplitude of the superimposed signal when there is flow; V max is the amplitude of the superimposed signal when there is no flow.

[0141] 3) Voltage difference flow measurement formula when the transmission signal is adjustable:

[0142] Usually, the amplitudes of the two ultrasonic signals of the forward and reverse flow cannot be completely consistent. At this time, if the transmission parameters of the two transmission transducers can be manually adjusted, the amplitudes of the two ultrasonic transducers can be consistent at the initial transmission. Here, the response amplitude of the piezoelectric ceramic is proportional to the amplitude of the excitation signal, and only the voltage of the excitation signal needs to be adjusted to adjust the response amplitude, so it is easy to adjust the amplitudes of the two signals to be consistent.

[0143] According to formula (6), the relationship between the time difference and the voltage difference is nonlinear. Therefore, the same time difference, but different initial conditions, the voltage difference obtained is different. In order to make the measurement result more accurate, the initial transmission time can be adjusted, that is, the time difference between the forward and reverse flow signals is artificially increased or decreased. But this requires that the measurement structure has the ability to adjust the transmission time, such as Figure 3 The structure shown. Assuming that the delay of the ultrasonic excitation signal is adjusted, a time difference will be generated between the two signals, and the voltage signal after the artificial delay t delay is shown as formula (11):

[0144]

[0145] Assuming no flow in the pipe at this time, the two signals will be superimposed without the influence of flow, according to the above process, it is obvious that

[0146] V start = V + (t) + V - (t) = V x ·2cos(ωt delay ) x(t) (12)

[0147] In the formula, V start is the initial amplitude of the voltage after the preset delay without flow.

[0148] If the signal is further artificially delayed by the time difference caused by flow, the voltage amplitude of the superimposed signal at this time can be considered as V end .

[0149] V end = V + (t+Δt) + V - (t-Δt) = V x ·2cos(ω(t delay +Δt)) x(t) (13)

[0150] It can be seen from the result that the voltage difference caused by flow to the signal is a function of its manual delay setting

[0151] ΔV(t) = V x ·X3(cos(ω(t delay +Δt) - cos(ωt delay )) (14)

[0152] Derive the delay time to obtain the maximum value of the function

[0153]

[0154] When

[0155]

[0156] The output voltage difference can obtain the maximum value

[0157] ΔV = V x ·X3(cos(nπ) - cos((-1) n+1 nπ-ωΔt) (17)

[0158] When the initial transmission delay of the transducer can be adjusted, the adjustment using the above formula can ensure that the voltage difference generated each time is the maximum voltage difference that the measuring device can generate under the current flow rate, resulting in better measurement performance. However, in practical applications, the exact time difference needs to be known in advance to calculate the delay. Therefore, an iterative method is introduced to adjust the initial delay. Considering the case where no initial delay is set, a time difference with acceptable accuracy can be obtained through the voltage amplitude difference. Considering that the adjustment accuracy of the transmitting equipment for the delay is limited, it cannot be exactly equal to the actual transmission time difference. Therefore, a further improved detection method is as follows:

[0159] S201. Without setting a delay time for the two transmitted signals, the voltage amplitude difference obtained is converted into a signal time difference using equation (6).

[0160] S202. Calculate the delay using equation (16), add the delay time, and retransmit the signal to obtain V. start size.

[0161] S203, Measurement of V end size.

[0162] Additionally, V start In practical applications, this measurement is impossible because it requires measurement without flow. However, according to V... max formula

[0163]

[0164] It can be seen that V max With V start The only difference between them is cos(ωt) delay The coefficients are determined. Therefore, the results can be quickly obtained through theoretical calculation methods. When V is obtained... max Then, V under arbitrary delay conditions start All can be calculated using equation (18).

[0165] Therefore, the formula for flow measurement using the voltage difference method under adjustable conditions is obtained:

[0166]

[0167] In the formula, θ is an intermediate variable used only for ease of calculation, and the unit is angle. When calculating the angle by inversely using trigonometric function values, the angle determined by a single inverse function is not unique. Therefore, the formula needs to be derived from the inverse functions of two trigonometric functions, cos... -1 and sin -1 Together, we determine a unique value.

[0168] The key technology of this invention lies in:

[0169] 1. Voltage difference method ultrasonic flow detection method. Voltage difference method is suitable for a wide range of flow detection scenarios, whether it is a pipe section, plug-in or externally clamped installation method can use this measurement method. This method uses ultrasonic transducers to emit two directions of ultrasonic waves, one upstream and one downstream. Due to the flow of fluid, the upstream propagating ultrasonic wave reaches longer, and the downstream propagating ultrasonic wave reaches shorter, and the resulting propagation time difference contains the flow size information. But the time difference measurement is difficult and the two signals generally need to be measured separately, so the time difference measurement is not accurate enough, especially in the case of small flow.

[0170] The method uses a piezoelectric ceramic to receive two ultrasonic signals at the same time, and the time difference information of the two signals is converted into voltage difference information, and the measurement formula (7) is obtained. The voltage measurement device has low cost and high measurement accuracy, and is a more suitable measurement method for high precision and low cost.

[0171] 2. Voltage difference method ultrasonic flow detection method adjusted according to actual conditions. Under non-ideal conditions, the transmitted ultrasonic signal can be adjusted according to whether the parameters are adjusted respectively, and the voltage difference method ultrasonic flow detection method can be divided into two categories.

[0172] A) For non-adjustable transmitted signals, the measurement formula is shown in formula (10), and the measurement method is:

[0173] (1) Receive two transmitted signals by the receiving piezoelectric ceramic, measure the amplitude M, N and delay Δt of the two received signals m relationship, obtain the exact amplitude ratio K and time delay Δt m .

[0174] (2) Substitute the measurement results of V end , V max , K, Δt m into formula (10) to obtain the final flow.

[0175] B) For adjustable transmitted signals, the measurement formula is shown in formula (19), and the measurement method is:

[0176] (1) Receive two transmitted signals by the receiving piezoelectric ceramic, and observe the amplitude relationship of the two received signals, adjust the amplitude of the excitation signal and retransmit. Use the proportional relationship between the excitation signal and the received signal to adjust the two received signals to the same amplitude. This process is a process of artificially adjusting the voltage of the excitation signal. The specific values of the amplitudes of the two ultrasonic signals do not affect the subsequent calculation, and only need to ensure that the amplitudes of the two ultrasonic signals are consistent after adjustment.

[0177] (2) Adjust the time delay of the excitation signal to make the two received signals reach the piezoelectric ceramic at the same time in the absence of flow in the pipeline, eliminating the time difference caused by circuit delay and other external factors. Similar to step (1) in category B), this time delay can be directly eliminated by manual adjustment, and its specific value does not affect subsequent calculations. It only needs to be adjusted to the point where the two ultrasonic signals are received by the piezoelectric ceramic at the same time in the absence of flow.

[0178] (3) Based on the previous two steps, the amplitude difference and time difference of the two ultrasonic signals are eliminated by adjusting the excitation signal. Therefore, when measuring the flow, it can be done in an ideal form, i.e., the ultrasonic signal amplitude, time, and shape are completely consistent. The flow measurement formula under the ideal condition, i.e., equation (7), can be used to obtain the first measurement of the flow. According to equation (6), the signal time difference Δt generated by the flow can be obtained.

[0179] (4) To further increase the measurement accuracy, use the time difference Δt obtained in the previous step (3) to calculate t delay using equation (16). delay As the excitation signal delay to re-excite the piezoelectric ceramic, the two ultrasonic signals are as shown in equation (11). The voltages V start and V end are re-measured, where V start can be indirectly measured by V max through equation (18).

[0180] (5) The final flow is obtained according to equation (19).

[0181] An experimental device as shown in Figure 6 is used to verify the flow detection effect of the time difference method. The excitation signal is a sine wave with a frequency of 4 MHz and a peak-to-peak value of 10 V. The excitation length is 20 cycles. The voltage difference method uses the transducer commonly used in the time difference method as the transmitting transducer. The horizontal receiving distance between the two transmitting transducers and the receiving transducer is the same, which can ensure that the ultrasonic waves produce the correct time difference after passing through the upstream and downstream liquids. During the receiving process, the receiving end uses a band-pass filter to filter the signal, and the amplification gain is set to 52 dB. The flow is calculated by measuring the voltage amplitude difference, and the final result is obtained by averaging multiple measurements.

[0182] The voltage difference amplitude can be enhanced by equation (17) as shown in Figure 7 . The final flow measurement error is shown in Figure 8 .

[0183] The above calculation examples of the present application are only used to illustrate the calculation model and calculation process of the present application, and are not used to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and all the embodiments cannot be exhausted here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A voltage difference ultrasonic flow detection method, characterized in that, Fluid detection is based on a transducer, using a piezoelectric ceramic to simultaneously receive two ultrasonic signals, one flowing in the same direction and the other in the opposite direction. The collected voltage signal V is then used for detection. end and V max The flow rate is obtained according to the first measurement formula; First measurement formula: In the formula, Q is the flow rate; K x This is the correction factor; k is the number of times the ultrasound wave propagates in a straight line in the liquid, and one "V"-shaped reflection in the pipe is counted as two straight-line propagations; R is the pipe radius; c l φ is the ultrasonic velocity in the liquid; φ is the angle between the ultrasonic trajectory on the liquid side and the interface, which is the interface between the pipe wall and the liquid; ω is the resonant frequency of the piezoelectric ceramic; V end The magnitude of the superimposed signal voltage when there is flow; V max It refers to the magnitude of the superimposed signal voltage when there is no flow.

2. The voltage difference ultrasonic flow detection method according to claim 1, characterized in that, The correction coefficient n is a constant related to the Reynolds number.

3. The voltage difference ultrasonic flow detection method according to claim 1 or 2, characterized in that, The first measurement formula was derived through the following process: Based on the characteristics of Fourier decomposition, the displacement equation for piezoelectric ceramic vibration is determined. Based on the steady-state response, the vibration solution of the piezoelectric ceramic is simplified to... In the formula, m is the mass of the piezoelectric ceramic; c is the damping coefficient; k is the stiffness; x(t) is the displacement of the piezoelectric ceramic; and t is time. i is the imaginary unit, A represents the amplitude of the sine wave, and ω is the inherent resonant frequency of the piezoelectric ceramic. Solving the equations, we obtain the forced vibration response as follows: x(t)=S1exp((-ξ1+ξ2)t)+S2exp((-ξ1-ξ2)t)+(X2+iX1)exp(-iωt)+(X2-iX1)exp(iωt) The forward and reverse ultrasonic signals are denoted as x(t+Δt) and x(t-Δt), respectively. A piezoelectric ceramic is used to simultaneously receive the two ultrasonic signals from the forward and reverse flows. Both ultrasonic signals are considered to be in the direction of their resultant force, i.e., they are directly added together. In the steady-state voltage response, we have: V(t)=V x ·x(t) In the formula, V(t) is a function of the steady-state voltage response, V x V is the coefficient; end The magnitude of the superimposed signal voltage when there is flow; V max It refers to the magnitude of the superimposed signal voltage when there is no flow.

4. A voltage difference ultrasonic flow detection method, characterized in that, To address the issue of unadjustable transducer transmission signals, a piezoelectric ceramic is used to simultaneously receive two ultrasonic signals, one flowing with the current and the other against it, based on the transducer's ability to detect fluid flow. The amplitudes M and N of the two received signals are measured to obtain K = N / M and the time delay Δt, which indicates that the two ultrasonic waves cannot arrive completely simultaneously. m According to V end V max K, Δt m The flow rate is obtained using the second measurement formula; Second measurement formula: In the formula, Q is the flow rate; K x This is the correction factor; k is the number of times the ultrasound wave propagates in a straight line in the liquid, and one "V"-shaped reflection in the pipe is counted as two straight-line propagations; R is the pipe radius; c l φ is the ultrasonic velocity in the liquid; φ is the angle between the ultrasonic trajectory on the liquid side and the interface, which is the interface between the pipe wall and the liquid; ω is the resonant frequency of the piezoelectric ceramic; V end The magnitude of the superimposed signal voltage when there is flow; V max It refers to the magnitude of the superimposed signal voltage when there is no flow.

5. The voltage difference ultrasonic flow detection method according to claim 4, characterized in that, The correction coefficient n is a constant related to the Reynolds number.

6. A voltage difference ultrasonic flow detection method according to claim 4 or 5, characterized in that, The second measurement formula was derived through the following process: First, the first measurement formula is derived and determined: When the transmission time is not adjustable, the two simultaneously emitted ultrasonic waves cannot arrive at the same time, resulting in a time delay Δt. m The formula for compensation is determined as follows: For the case where the amplitudes of the two received signals, one with the current current and one with the opposite current, are not adjustable, let the current signals be M·x(t-Δt) and N·x(t+Δt), where M and N represent their respective amplitudes. The resulting superimposed signal is: K = N / M By determining K, flow measurement is then performed using the voltage difference; subsequently, the second measurement formula is determined. Among them, V end The magnitude of the superimposed signal voltage when there is flow; V max It refers to the magnitude of the superimposed signal voltage when there is no flow.

7. A voltage difference ultrasonic flow detection method, characterized in that, For cases where the transducer's transmitted signals are individually adjustable, fluid detection is performed based on the transducer. A piezoelectric ceramic simultaneously receives two ultrasonic signals, one flowing with the current and the other against it. The detection process includes the following steps: (1) Receive the two transmitted signals by the receiving piezoelectric ceramic, observe the amplitude relationship between the two received signals, adjust the amplitude of the excitation signal and retransmit; adjust the amplitude of the two received signals to be consistent. (2) Adjust the delay time so that the two received signals can reach the piezoelectric ceramic simultaneously when there is no flow in the pipe; (3) Based on the first two steps, the excitation signal was adjusted to eliminate the amplitude difference and time difference between the two ultrasonic waves; when measuring the flow rate, the flow rate was measured according to the first measurement formula to obtain the flow rate of the first measurement. First measurement formula: In the formula, Q is the flow rate; K x This is the correction factor; k is the number of times the ultrasound wave propagates in a straight line in the liquid, and one "V"-shaped reflection in the pipe is counted as two straight-line propagations; R is the pipe radius; c l φ is the ultrasonic velocity in the liquid; φ is the angle between the ultrasonic trajectory on the liquid side and the interface, which is the interface between the pipe wall and the liquid; ω is the resonant frequency of the piezoelectric ceramic; V end The magnitude of the superimposed signal voltage when there is flow; V max It is the magnitude of the superimposed signal voltage when there is no flow. according to The signal time difference Δt generated by the flow is obtained; (4) Based on the time difference Δt, using The artificial delay t was calculated. delay , will t delay The piezoelectric ceramic is re-excited by delaying the excitation signal, resulting in the following two ultrasonic signals: V + (t)=V(t+t delay ) V - (t)=V(t-t delay ) Remeasure voltage V start and V end size; (5) Obtain the final flow rate according to the third measurement formula; Third measurement formula: Where θ is an intermediate variable, θ is determined by and A unique value is determined jointly.

8. The voltage difference ultrasonic flow detection method according to claim 7, characterized in that, In step (4), the voltage V is measured again. start and V end When the size is V start Through V start =cos(ωt) delay )·V max Obtained through indirect measurement.

9. The voltage difference ultrasonic flow detection method according to claim 7, characterized in that, The correction coefficient n is a constant related to the Reynolds number.

10. A voltage difference ultrasonic flow detection method according to any one of claims 7 to 9, characterized in that, The third measurement formula was derived through the following process: First, the first measurement formula is derived and determined: In the process of deriving and determining the first measurement formula, we obtain This leads to the conclusion that the relationship between time difference and voltage difference is non-linear. The delay of the ultrasonic excitation signal is adjusted based on the artificial delay t. delay The voltage signal obtained is as follows: V + (t)=V(t+t delay ) V - (t)=V(t-t delay ) When there is no flow in the pipe, the two signals will be superimposed without being affected by the flow rate: V start =V + (t)+V - (t)=V x ·2cos(ωt delay )x(t) In the formula, V start It presets the initial voltage amplitude under no flow after a delay; The artificially delayed signal experiences a time difference due to the flow rate. The magnitude of the superimposed signal voltage V at this point, when there is flow, is... end Become V end =V + (t+Δt)+V - (t-Δt)=V x ·2cos(ω(t delay +Δt))x(t) The results show that the voltage difference in the signal caused by the flow rate is a function of the artificial delay. Taking the derivative with respect to the delay time to obtain the maximum value of the function yields... The output voltage difference reaches its maximum value. ΔV=V x ·X3(cos(nπ)-cos((-1) n+1 nπ-ωΔt) With the initial transmission delay of the transducer adjustable, the above formula ensures that the voltage difference generated each time is the maximum voltage difference that the measuring device can generate under the current flow rate; thus, the third measurement formula is determined. In the formula, θ is an intermediate variable, derived from... and A unique value is determined jointly.

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