CN117213570A - Flow measurement equipment and method based on CMUT device - Google Patents

Abstract

The invention discloses a flow measurement device and method based on a CMUT device, which relates to the technical field of flow measurement. Its structure includes a fluid conduction component that transports media along a first direction. The fluid conduction component includes at least two flow measurement points, with different flow measurement points. The flow measurement points are located at different positions in the first direction, and a sensor system is arranged at the position of the flow measurement point. The sensor system includes an ultrasonic probe module. The ultrasonic probe module consists of an upper electrode, a vibrating film, an insulating layer, and a silicon substrate. It is composed of a lower electrode stacked in sequence, and a first cavity is opened on the side of the insulating layer close to the upper electrode. Compared with the existing technology, the structure of the flow detection device in the present invention is relatively simple, and the method used is more sensitive. high.

Description

A flow measurement equipment and method based on CMUT device

Technical field

The present invention relates to the technical field of flow measurement, and in particular to a flow measurement equipment and method based on a CMUT device.

Background technique

With the rapid development of my country's industrial society and the continuous development of economy and technology, various industries have gradually introduced high-precision, high-security, high-reliability, intelligent and digital automated instrumentation and equipment to improve my country's industrial production and economic benefits. An important foundation was laid. As an important technology in the engineering field, flow measurement is also an important parameter in the industrial production process. It has important value that cannot be ignored in many aspects such as statistical settlement, balance analysis, energy observation, utilization and monitoring. Therefore, flowmeters, as instruments and equipment for measuring fluid flow velocity and flow, have been widely used in petrochemical industry, disaster warning, civil measuring instruments and other fields, and have played an important role in ensuring product quality, improving production efficiency, and promoting the development of science and technology.

As a new type of flow meter, ultrasonic flow meters have the advantages of no pressure loss, no mechanical parts, non-contact, high precision, and intelligence compared to traditional flow meters. Compared with similar foreign products, domestic ultrasonic flowmeters are cheaper, but there are certain gaps in measurement accuracy, installation environment applicability, and result reliability. Ultrasonic transducers are key components of ultrasonic detection technology. Ultrasonic transducers based on the piezoelectric principle are currently widely used. However, piezoelectric ultrasonic transducers have shortcomings such as narrow bandwidth and low sensitivity, and there are development bottlenecks.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a flow measurement device and method based on a CMUT device. Compared with the existing technology, the structure of the flow detection device in the present invention is relatively simple, and the method used is sensitive. higher.

The present invention is realized through the following technical solutions: The present invention discloses a flow measurement device based on a CMUT device, which includes a fluid conduction component that transports media along a first direction. The fluid conduction component includes at least two flow measurement points, with different flow measurement points. The flow measurement points are located at different positions in the first direction, and a sensor system is arranged at the position of the flow measurement point. The sensor system includes an ultrasonic probe module. The ultrasonic probe module consists of an upper electrode, a vibrating film, an insulating layer, a silicon substrate and a The lower electrodes are stacked in sequence, and a first cavity is opened on the side of the insulation layer close to the upper electrode.

Preferably, the sensor system further includes:

A power module, which performs step-up, step-down and reverse voltage transformation of DC power to meet the power requirements of each module of the sensor system;

CMUT drive module, the CMUT drive module receives the control signal, emits and receives the first sound wave;

The second sound wave received by the ultrasonic probe module transmits the second sound wave to the signal conditioning module;

A signal conditioning module, which performs signal processing on the second acoustic wave to obtain a conditioned signal;

Control and data processing module, the control and processing signal processing module processes the conditioning signal;

Wherein, the control and data processing module includes a cross-correlation algorithm module, a timing module and a controller module.

This application also discloses a flow measurement method based on an ultrasonic transducer, which is executed on a flow measurement device. The measurement method includes the steps:

Read the parsing limit configuration information, generate a PWM square wave to control the analog switch, and generate the required driving square wave;

Send a driving square wave to act on the sensor system to complete the ultrasonic signal transmission;

The signals received by the sensor system are collected by ADC, transmitted and filtered by DMA;

After receiving a pair of ultrasonic signals, interpolation and cross-correlation operations are performed on the two signals to calculate the time of flight difference;

When the measurement period is reached, all the obtained data are processed to calculate the flow rate and volumetric flow rate;

After a delay, the system starts measuring again and completes the flow measurement.

Preferably, sending the driving square wave includes the steps:

Perform timer cascade settings and generate PWM pulse signals through the timer;

PWM pulse serves as the control end of the analog switch;

The NO and NC terminals of the analog switch are connected to 0V and 24V voltages respectively;

Generate a specified number of 24V to 0V driving square waves through the COM terminal;

The driving square wave from 24V to 0V acts on the sensor system through the analog switch to complete the driving square wave transmission.

The invention discloses a flow measurement equipment and method based on a CMUT device. Compared with the existing technology:

The ultrasonic probe module of the present invention realizes accurate measurement of flow. Based on the fact that the switch of the ultrasonic probe module is closed in the transmitting mode, the vibrating film vibrates under the action of DC bias voltage and AC excitation voltage, thereby causing the medium in the sound field to vibrate and realizing the arrival of electrical signals. Conversion of acoustic wave signals; when the CMUT works in the receiving mode, the switch is turned off, the DC bias voltage fills the capacitor with charge, and the ultrasonic signal acts on the vibrating film to vibrate, causing the electrodes on the surface of the vibrating film to also vibrate, causing the charge of the capacitor to change. The change generates current and realizes the conversion technology of acoustic signal to electrical signal. The present invention measures flow through CMUT sensor, achieves miniaturization and low cost, and improves the consistency level of the instrument. In addition, the excitation method of the CMUT sensor itself is different from that of traditional piezoelectric ultrasound, and there are also certain differences in circuit design. The traditional method is sine wave excitation, but the CMUT sensor needs to add a DC voltage bias to the sine and square wave excitation. Therefore, the CMUT drive module of the present invention needs to generate a PWM square wave to control the analog switch to complete the transmission of the driving square wave. In short, the present invention aims to provide a flow measurement method and device based on a CMUT sensor, which has the advantages of high accuracy, good stability, and high reliability, and has broad application prospects in the field of flow detection.

Description of the drawings

Figure 1 is a schematic structural diagram of the flow measurement device in the present invention;

Figure 2 is a schematic structural diagram of an ultrasonic probe module in an embodiment;

Figure 3 is a schematic diagram of the layout of the pipe wall and ultrasonic probe module in one embodiment;

Figure 4 is a circuit diagram of a driving module in an embodiment;

Figure 5 is a signal conditioning circuit diagram in an embodiment;

Figure 6 is a block diagram of system design ideas in an embodiment;

Figure 7 is a system software control flow in an embodiment;

Figure 8 is a signal waveform diagram in an embodiment;

Figure 9 is a signal waveform diagram after signal interpolation in an embodiment;

Figure 10 is a schematic diagram of flight time calculation in an embodiment.

Detailed ways

The following is a detailed description of the embodiments of the present invention. This embodiment is implemented based on the technical solution of the present invention and provides detailed implementation modes and specific operating processes. However, the protection scope of the present invention is not limited to the following implementations. example.

As shown in Figure 1, the present invention is implemented through the following technical solutions: The present invention discloses a flow measurement device based on a CMUT device, including a fluid conduction component 1 that transports media along a first direction. The fluid conduction component 1 includes at least There are two flow measurement points. The different flow measurement points are located at different positions in the first direction. A sensor system 2 is arranged at the position of the flow measurement point. As shown in Figure 2, the sensor system 2 includes an ultrasonic probe module. The probe module is composed of an upper electrode 26, a vibrating film 25, an insulating layer 23, a silicon substrate 22 and a lower electrode 21 stacked in sequence. The insulating layer 23 has a first cavity 24 on a side close to the upper electrode 26.

According to the different excitation signals when the ultrasonic probe module works, its working mode can be divided into transmitting mode and receiving mode. The ultrasonic probe module is CMUT (Capacitive micromachined ultrasonic transducers). When the CMUT works in the transmitting mode, the switch is closed and the vibrating film is biased in DC. Vibration is generated under the action of voltage and AC excitation voltage, which causes the vibration of the medium in the sound field and realizes the conversion of electrical signals to acoustic signals; when the CMUT works in the receiving mode, the switch is turned off, the DC bias voltage fills the capacitor with charge, and the ultrasonic signal acts on The vibrating film vibrates, causing the electrodes on the surface of the vibrating film to also vibrate, causing changes in the charge of the capacitor to generate current, thereby converting acoustic signals into electrical signals. Among them, the CMUT sensor in the present invention is used as a MEMS (micro-electromechanical system) sensor for flow detection. It is a non-contact sensor that uses capacitive micro-mechanical shock absorbers to identify the flow rate, turbulence and pressure of the fluid, thereby improving the measurement accuracy, miniaturizing the product and making the cost low. The CMUT sensor excitation method has a higher degree of frequency modulation than piezoelectric ultrasonic excitation. It puts low frequency and high frequency in one signal, and when it is excited to oscillate, it will have larger emission energy, so that small fluid changes can be effectively detected. Compared with the traditional sine and square wave excitation, the CMUT excitation circuit design adds a DC voltage bias, so that the excited oscillation increases the voltage bias, which in turn makes the ultrasonic emission have greater energy, thereby improving the flow detection accuracy. For the work of the CMUT sensor The principle is based on the reflection principle of ultrasonic waves. When the CMUT sensor emits ultrasonic waves, it produces vibrations of a certain amplitude and frequency. These vibrations are transmitted forward and trigger ultrasonic waves that are reflected back from the surface of the object being measured. The sensor receives the reflected ultrasonic waves and converts them into electrical signals. Then, the electrical signal is processed and analyzed to determine the distance, speed, shape and other parameters of the measured object. The CMUT sensor in the present invention has many advantages, such as sensitivity, accuracy, easy manufacturing and integration, small size, low power consumption and Lower cost.

The CMUT-based ultrasonic flowmeter uses the transit time method as the basic principle of measurement. When the ultrasonic beam propagates in the fluid, due to the superposition of the ultrasonic speed and the fluid flow speed in the velocity field, the ultrasonic beam follows the fluid flow direction within the same distance. The length of time it takes to propagate is different from that of propagation against the direction of fluid flow. It takes a shorter time to propagate with the flow and a longer time to propagate against the flow. The transit-time ultrasonic flowmeter calculates the instantaneous flow velocity of the fluid by measuring the time difference between the downstream and counterflow of the ultrasonic beam.

For example, as shown in Figure 3, two ultrasonic probe modules are installed upstream and downstream of the pipe wall to take turns transmitting and receiving ultrasonic pulse signals. The channel length is L, the pipe diameter is D, and the channel angle is 0°. . The following formula can be obtained:

Among them, Q is the instantaneous flow rate, v is the average velocity of the fluid on the vocal tract line, Δt is the flight time difference, t ₁ and t ₂ represent the flight time up and down respectively, and k is the flow correction coefficient. The above calculation method is no longer associated with the ultrasonic propagation speed c, which can avoid the ultrasonic flow measurement accuracy being affected by changes in the temperature of the liquid being measured.

For the CMUT device in the present invention, the CMUT device has more advantages than the traditional piezoelectric ultrasonic sensor. First, the frequency response range of the CMUT device is wider. This is because the structure and working principle of the CMUT device are different from those of traditional piezoelectric ultrasonic sensors. Ultrasonic sensors are different. The CMUT device is an ultrasonic sensor based on microelectromechanical systems (MEMS) technology. It is composed of a set of tiny capacitors. When the capacitor is exposed to an external ultrasonic signal, it will produce tiny vibrations, thereby converting the ultrasonic signal into electric signal. Since the structure and working principle of the CMUT device are different from traditional piezoelectric ultrasonic sensors, it can operate in a higher frequency range and achieve higher resolution and sensitivity. Secondly, CMUT devices have higher energy conversion efficiency. Traditional piezoelectric ultrasonic sensors convert mechanical energy into electrical energy through the piezoelectric effect, so their energy conversion efficiency is low. The CMUT device converts mechanical energy into electrical energy through capacitance changes, so its energy conversion efficiency is higher and it can achieve higher signal-to-noise ratio and detection sensitivity. Third, CMUT devices have smaller size and weight. Since CMUT devices are manufactured based on microelectromechanical systems (MEMS) technology, they can be manufactured at the micron level, have smaller size and weight, and can be easily integrated into various devices. Fourth, CMUT devices have lower power consumption. Because the energy conversion efficiency of CMUT devices is higher, its power consumption is lower than traditional piezoelectric ultrasonic sensors, which can achieve longer battery life and lower energy consumption. Fifth, CMUT devices have higher reliability and stability. Because the manufacturing process of CMUT devices is more precise and controllable than traditional piezoelectric ultrasonic sensors, higher reliability and stability can be achieved.

In one embodiment, the pipe diameter is small, and the ultrasonic transducer is installed in a mouth shape. Place a pair of ultrasonic transducers at both ends of the pipeline. The transducers are in direct contact with the fluid. Use sealing rings to ensure the sealing between the pipeline and the transducers. The actual installation is shown in Figure 1;

Among them, as shown in Figure 2, the sensor system 2 also includes: a power module, which performs step-up, step-down and reverse voltage transformation of DC power to meet the power requirements of each module of the sensor system 2; a CMUT drive module, so The CMUT drive module receives the control signal, transmits and receives the first sound wave; the second sound wave received by the ultrasonic probe module transmits the second sound wave to the signal conditioning module; the signal conditioning module, the signal conditioning module controls the second sound wave. The sound wave performs signal processing to obtain a conditioning signal; a control and data processing module processes the conditioning signal; wherein the control and data processing module includes a cross-correlation algorithm module, a timing module and a controller module.

In one embodiment, the system adopts a modular design concept. As shown in Figure 6, the system is divided into four major modules. Each module has division of labor functions, and the core controller completes the collection and processing of information. The system structure is shown in the figure below. The power module performs operations such as step-up, step-down and reverse transformation of DC power to meet the power requirements of each module of the system; the CMUT drive module completes the transmission and reception of sound waves under the control of the excitation pulse signal. The sound waves received by the ultrasonic probe will undergo signal conversion, filtering and other operations in the signal conditioning module; the conditioned signal enters the control and data processing module, where the cross-correlation algorithm module performs cross-correlation operations to obtain the maximum signal matching. point, the timing module stops timing and completes the ultrasonic transit time measurement; the microcontroller reads the time information, the microcontroller records and calculates the transit time difference, and then calculates the liquid flow rate and displays it on the screen.

Specifically, the core control chip used in the detection system is the STM32F407ZGT6 microcontroller, and the center frequency of the CMUT ultrasonic probe used is 1MHz. The chip has a powerful configuration, rich internal resources, integrates FPU and DSP instructions, and has 192KB SRAM, 1024KB FLASH, 12 16-bit timers, 2 32-bit timers, 2 DMA controllers, 3 SPIs, 3 IICs, 6 serial ports, 3 12-bit ADCs, etc., which can meet the functional requirements of the system.

For the power module to perform operations such as boosting, bucking, and reverse transformation of DC power, the specific power supply requirements to be realized are: 3.3V power supply for the microcontroller, 24V driving voltage for the CMUT, and ±2.5V supply voltage for the signal conditioning circuit; CMUT driving A square wave is a certain number of square waves, with a low level of 0V and a high level of 24V. Use 2 analog switches to generate 2 sets of driving square waves, and use 2 analog switches to switch the sending and receiving modes of the 2 sets of signals. The analog switch model is MAX4649EKA. The analog switch can withstand a maximum voltage of 44V, which can meet the usage requirements. As shown in Figure 4, the control signals of the analog switches are all generated by the microcontroller. When U1 or U2 does not receive the command from the microcontroller to generate a drive signal, the analog switch outputs a high level, so that the ultrasonic transducer is under a DC bias voltage of 24V. , otherwise it will output a square wave signal. U4 and U5 are responsible for switching the ultrasonic probe's transmission/reception of ultrasonic signals. They are implemented by using a microcontroller to control the high and low levels of Switch1 and Switch2. When Switch1 or Switch2 is low level, the corresponding ultrasonic probe is in the transmitting state, and vice versa. The circuit diagram of the CMUT driver module is shown in Figure 4. For the signal conditioning module, the GS8092 chip is used as the core amplification circuit to amplify the received ultrasonic signal so that the signal can meet the processing requirements of the microcontroller. The reverse amplifier circuit has an amplification factor of 10k/100 = 100 times. The signal conditioning circuit diagram is shown in Figure 5.

Control and data processing module

The control and operation are realized using the microcontroller STM32F407. The STM32F407 has a DSP library capable of signal processing, which can quickly complete operations such as filtering, interpolation and Fourier transform of digital signals. The quantities that the microcontroller needs to calculate include flight time, flight time difference, fluid flow rate, volume flow, etc., and complete the display function of relevant information on the screen.

In one embodiment, in order for the ultrasonic flow measurement system to meet the functional requirements, not only a reasonable hardware foundation is required, but also a software control system capable of processing signal data in real time. Since the core controller selected for the ultrasonic flow measurement system is the STM32F407 microcontroller, the software control system is also designed on this hardware platform. The system software is developed using C language, the development environment is Keil uVision5, and the software is based on the library functions provided by ARM.

Analyze the functions to be realized by the measurement system. In order to improve the efficiency of program design and the reliability of program operation, the modular design concept is adopted and the system software is divided into main program module, drive pulse sending module, signal acquisition and processing module, human-computer interaction module. The main control module initializes and configures the program, including system clock configuration, timer configuration, I/O pin configuration, interrupt configuration, initialization of system parameters and other operations; the driver module implements the configuration of drive pulses and conversion of transceiver modes; signal acquisition and The processing module mainly completes functions such as signal collection, transmission, filtering, calculation and storage; the human-computer interaction module implements interactive functions such as buttons and display, as shown in Table 1.

Software module Function Main control module System clock configuration, timer configuration, I/O pin configuration, interrupt and DMA configuration, initialization parameters, etc. Driver module Drive pulse configuration, transceiver mode conversion Signal acquisition and processing module ADC data acquisition, DMA transmission, band-pass filtering, cross-correlation operation, spline interpolation, data storage, etc. Human-computer interaction module Key detection, function selection, content display

Form 1

This application also discloses a flow measurement method based on an ultrasonic transducer, which is executed on a flow measurement device. The measurement method includes the steps:

Read the parsing limit configuration information, generate a PWM square wave to control the analog switch, and generate the required driving square wave;

Send a driving square wave to act on the sensor system 2 to complete the ultrasonic signal transmission;

The signals received by the sensor system 2 are collected by ADC, transmitted by DMA and filtered;

After receiving a pair of ultrasonic signals, interpolation and cross-correlation operations are performed on the two signals to calculate the time of flight difference;

When the measurement period is reached, all the obtained data are processed to calculate the flow rate and volumetric flow rate;

After a delay, the system starts measuring again and completes the flow measurement.

In one embodiment, the system software control flow is shown in Figure 7. When the system starts running, it first performs an initialization operation. The software program instructs the microcontroller to read and parse limit configuration information, such as the number of pulses, measurement period, etc. Then start the measurement, and the timer generates a PWM square wave to control the analog switch, thereby generating the required driving square wave. The driving square wave acts on the ultrasonic transducer, and the ultrasonic signal emission on one side has been completed; then the ultrasonic transducer on the other end is The signal received by the transducer is collected by ADC, transmitted and filtered by DMA; after receiving a pair of ultrasonic signals, interpolation and cross-correlation operations are performed on the two signals to obtain the flight time difference, and the threshold comparison method can be used to obtain the single side flight time; when the measurement period is reached, all the obtained data are processed, the flow rate and volume flow rate are calculated, and the calculation results are displayed on the screen. After a delay, the system starts measuring again, and finally refreshes the measurement results on the screen.

For the timer cascade setting of the microcontroller, configure the advanced timer TIM1 as the master trigger mode, and use TIM1 to generate a 1MHz PWM pulse; configure the general TIM2 as the slave trigger mode, and set the number of pulses through TIM2, so that precise control can be achieved frequency and number of pulses. The channel of PWM pulse output is CH1, and the corresponding pin is PA11. The generated pulse serves as the control end of the analog switch, and the NO and NC ends of the analog switch are connected to 0V and 24V respectively. Therefore, a specified number of 24V ~ 0V driving square waves can be generated at the COM end. This driving square wave controls the transceiver mode. The analog switch acts on the ultrasonic transducer to complete the emission of ultrasonic waves.

The original data of the ultrasonic signal is collected using the high-speed ADC built into the STM32F407. Since the frequency of the ultrasonic signal collected is 1MHz, according to the sampling theorem, the ADC sampling frequency is at least 2MHz. In order to facilitate the processing of digital signals and improve the accuracy of measurement, the number of sampling points within a single signal cycle needs to be increased. For example, if a 1MHz signal is collected at a sampling frequency of 2MHz, 2 data points can be collected in a single signal cycle; while in a sampling frequency of 7MHz, 7 data points can be collected in a single signal cycle, and the collection results are closer to the real signal waveform. This article uses three ADCs in the STM32F407 microcontroller to alternately collect ultrasonic signals, with a maximum sampling frequency of 7.2MHz. When the ADC clock of STM32F407 is 36MHz and the ADC acquisition cycle is 3 ADC clock cycles, the sampling frequency of a single ADC reaches the maximum value of 2.4MHz. Therefore, to ensure that the sampling frequency of the ADC is 2.4MHZ, the system clock and ADC clock of the microcontroller must first be configured.

First, configure the microcontroller system clock to 144MHz. After dividing by 2, the APB2 clock is 72MHz. After dividing by 2, the ADC clock is 36MHz. A complete ADC acquisition includes a sampling phase and a data conversion phase. The sampling phase is set to 3 ADC clock cycles, and the conversion phase is 12 ADC clock cycles. A total of 15 ADC clock cycles are required. Therefore, the sampling frequency f of a single ADC is:

After configuring the triple ADC alternate acquisition mode, the ADC sampling frequency reaches 7.2MHz, and 7 to 8 points can be collected in a single cycle of the 1MHz ultrasonic signal, meeting the sampling requirements of the system.

Among them, sending a driving square wave includes the steps:

Step 1: Perform timer cascade settings and generate PWM pulse signals through the timer;

Step 2: PWM pulse serves as the control end of the analog switch;

Step 3: Connect the NO and NC terminals of the analog switch to 0V and 24V respectively;

Step 4: Generate a specified number of 24V to 0V driving square waves through the COM terminal;

Step 5: The driving square wave from 24V to 0V acts on the sensor system 2 through the analog switch to complete the driving square wave transmission.

For data processing and calculations

The data processing is mainly to obtain three important parameters such as the upstream flight time t _up , the downstream flight time t _dn , and the flight time difference Δt, and to indirectly calculate the flow rate and instantaneous flow rate of the fluid. The main steps include signal filtering, spline interpolation, time-of-flight calculation, cross-correlation operation, flow velocity and flow calculation.

(1) Signal filtering

In practice, a microcontroller is used to sample the signal, and anonymous host computer software is used to display the collected data in real time. As can be seen from the image on the left side of Figure 8, the signal waveform is chaotic and there is great interference. By analyzing the waveform of the collected received signal, it can be found that the amplitude of the 1MHz main frequency is not prominent. Therefore, in order to conveniently lock the waveform of the target signal, the original collected signal needs to be band-pass filtered before data processing. Use the DSP library that comes with STM32F407, set the cutoff frequencies in the filter parameters to 0.95MHz and 1.05MHz, use MATLAB software to generate filter parameters, and call the filter function arm_fir_f32_bp to filter the original data. The filtered received signal is more conducive to data processing. deal with. The image on the right in Figure 8 is the signal after software filtering by the microcontroller. The maximum signal amplitude after filtering is 700mV.

(2) Cubic spline interpolation

It can be seen from the filtered signal that most of the interference of the signal has been eliminated. There are about 10 waves in a signal, and there are 200 data collection points in total. The time interval between collection points is 0.1389us. In order to facilitate subsequent signal processing, cubic spline interpolation is used to interpolate 200 data points, increasing the number of data points to 1024. The specific method is to use the DSP library that comes with STM32F407, first call the function arm_spline_init_f32 to initialize the spline function, and then call the function arm_spline_f32 to calculate the spline function. Since the number of data points after interpolation is approximately 5 times the original, the time interval between signal data points after interpolation is approximately 1/5 of the original. The signal waveform diagram after signal interpolation is shown in Figure 9.

This application document calculates the upstream flight time t _fly by judging whether the data collected by the ADC crosses zero.

For the calculation of flight time, in Figure 10, t0 represents the signal sending time; t1 represents the ADC starting sampling time, and t2 represents the arrival time of the second wave of the echo signal. In order to reduce the impact of interference signals on the original acquisition signal and make the signal acquisition process more stable, the time when the ADC starts sampling should be as close as possible to the time when the first wave of the echo signal arrives. According to the calculation formula of flight time, the flight time t at static state (that is, the fluid flow rate is zero) can be calculated, as shown in Equation 4.1, from which the time when ADC1 starts working can be estimated.

According to the above formula, it can be seen that the upstream flight time t _up is less than the flight time t when the flow rate is zero, so the time t when starting ADC1 sampling should be 3us-5us earlier than the arrival time of the first wave of the echo signal. After the ADC1 sampling time t ₁ is determined, a timer is used to start timing from time t0. When the timing time is up, triple ADC alternate sampling can be started from time t1, and the collected data is transferred to the memory by DMA for data processing. In the process of data collection, the voltage of each collection point of the original signal is obtained. When it is found that the voltage of two consecutive points is negative and then the voltage of two consecutive points is positive, the program considers that there is a zero-crossing point from negative to positive, and the zero-crossing point Must be located between two adjacent collection points with opposite polarity. Between these two adjacent points, cubic spline interpolation is further used for fitting, and the zero-crossing point of the echo signal from negative to positive can be obtained. According to Figure 10, it can be seen that since the signal before the first wave is zero, the collected data will not change from negative to positive. The zero crossing point from negative to positive judged by the program must correspond to the second wave from negative to positive. Positive zero crossing. In Figure 10, the arrival time of the second wave of the echo signal is t2. Since the echo signal frequency is 1MHz, each waveform period is 1us, from which the flight time can be calculated:

t _fly =t ₂ -t ₁ -1

According to this method, the upstream flight time t _up and the downstream flight time t _dn can be calculated. Since the flight time difference has a great influence on the calculation results, the cross-correlation algorithm is used to accurately calculate the flight time difference.

(4)Flight time difference calculation

After obtaining the upstream and downstream flight times, in order to accurately obtain the flight time difference, the discrete cross-correlation algorithm is used for the two sets of filtered signal data. First, perform FFT transformation on the two sets of filtered signals corresponding to the upstream and downstream to convert the time domain signal into the frequency domain; then conjugate the downstream filtered frequency domain signal, and multiply the result with the upstream filtered frequency domain signal to get The frequency domain output of the discrete mutual function; then use IFFT to convert the frequency domain output of the discrete mutual function into a time domain output. In order to calculate the results more accurately, after calculating the discrete cross-correlation function, the cubic spline interpolation method is used to interpolate the area near the maximum point, and the abscissa corresponding to the true maximum point is obtained, which is the time of flight difference.

(5) Calculation of flow rate and flow rate

Since the small deviation of the flight time difference has a great impact on the calculation results, in order to reduce the measurement error, one measurement cycle in this application document includes multiple measurements of the flight time difference. Store the results of multiple measurements in an array in ascending order, remove the maximum and minimum values from the numerical elements, find the standard deviation of the remaining array elements, and then remove the elements in the array that have a greater impact on the standard deviation. The remaining array elements are averaged, which is the average flight time difference Δt within a measurement period. In the same way, the average upstream flight time t _up and the average downstream flight time t _dn within a measurement period are calculated, and the average flow velocity v and instantaneous flow rate Q of the fluid are calculated.

In summary, for the ultrasonic probe module of the present invention to achieve accurate flow measurement, based on the fact that the switch of the ultrasonic probe module is closed in the transmitting mode, the vibrating film vibrates under the action of DC bias voltage and AC excitation voltage, thereby causing the medium in the sound field to vibrate. Realize the conversion of electrical signals to acoustic signals; when the CMUT works in the receiving mode, the switch is turned off, the DC bias voltage fills the capacitor with charge, and the ultrasonic signal acts on the vibrating film to vibrate, causing the electrodes on the surface of the vibrating film to also vibrate. Causes changes in the charge of the capacitor to generate current, realizing the conversion of acoustic signals into electrical signals.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can, within the technical scope disclosed in the present invention, use the technical solutions of the present invention and its Equivalent substitutions or changes of the inventive concept shall be included in the protection scope of the present invention.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations There is no such actual relationship or sequence between them. Furthermore, the terms "comprises," "comprises," or any other variations thereof are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also those not expressly listed other elements, or elements inherent to the process, method, article or equipment. Without further limitation, an element defined by the statement "comprises a..." does not exclude the presence of additional identical elements in a process, method, article, or apparatus that includes the stated element.

Claims (5)

1. A flow measurement device based on a CMUT device, characterized in that it includes a fluid conduction component that transports media along a first direction, and the fluid conduction component includes at least two flow measurement points, and different flow measurement points are located at the first At different positions in the direction, a sensor system is arranged at the flow measurement point. The sensor system is composed of a CMUT sensor based on a micro-motor system. The CMUT sensor consists of an upper electrode, a vibrating film, an insulating layer, a silicon substrate and a lower electrode in sequence. Composed in a stack, a first cavity is opened on the side of the insulating layer 23 close to the upper electrode; Among them, the distance between the two flow detection points is L, the diameter of the fluid conduction component is D, the sound channel angle is 0°, Q is the instantaneous flow rate, v is the average speed of the fluid on the sound channel line, Δt is the flight time difference, t ₁ and t ₂ represent the upstream and downstream flight times respectively, and k is the flow correction coefficient, which satisfies the following formula: The sound channel angle is the angle between the ultrasonic propagation direction and the fluid flow direction, and the flight time is the time between ultrasonic transmission at one flow detection point and ultrasonic reception at another flow detection point. 2. A flow measurement device based on a CMUT device as claimed in claim 1, characterized in that the sensor system 2 further includes: A power module, which performs step-up, step-down and reverse voltage transformation of DC power to meet the power requirements of each module of the sensor system; CMUT drive module, the CMUT drive module receives the control signal and emits the first sound wave; the second sound wave received by the ultrasonic probe transmits the second sound wave to the signal conditioning module; A signal conditioning module, which performs signal processing on the second acoustic wave to obtain a conditioned signal; Control and data processing module, the control and processing signal processing module processes the conditioning signal; Wherein, the control and data processing module includes a cross-correlation algorithm module, a timing module and a controller module. 3. A flow measurement method based on an ultrasonic transducer, characterized by executing the flow measurement device according to claim 1. 4. A flow measurement method based on an ultrasonic transducer as claimed in claim 3, characterized in that the measurement method includes the steps: Read the parsing limit configuration information, generate a PWM square wave to control the analog switch, and generate the required driving square wave; Send a driving square wave to act on the sensor system to complete the ultrasonic signal transmission; The signals received by the sensor system are collected by ADC, transmitted and filtered by DMA; After receiving a pair of ultrasonic signals, interpolation and cross-correlation operations are performed on the two signals to calculate the time of flight difference; When the measurement period is reached, all the obtained data are processed to calculate the flow rate and volumetric flow rate; After a delay, the system starts measuring again and completes the flow measurement. 5. A flow measurement method based on an ultrasonic transducer as claimed in claim 3, characterized in that sending a driving square wave includes the steps: Perform timer cascade settings and generate PWM pulse signals through the timer; PWM pulse serves as the control end of the analog switch; The NO and NC terminals of the analog switch are connected to 0V and 24V voltages respectively; Generate a specified number of 24V to 0V driving square waves through the COM terminal; The driving square wave from 24V to 0V acts on the sensor system 2 through the analog switch to complete the driving square wave transmission.