CN115248250A - Device and method for precisely measuring liquid concentration based on SOPC - Google Patents
Device and method for precisely measuring liquid concentration based on SOPC Download PDFInfo
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Abstract
A device and a method for precisely measuring liquid concentration based on SOPC are composed of an ultrasonic transducer group, an ultrasonic signal generating circuit, an ultrasonic echo signal processing circuit and an online temperature measuring circuit. The ultrasonic transducer group consists of a plurality of groups of paired transducers, the ultrasonic signal generating circuit is used for driving the ultrasonic transducers to generate ultrasonic signals, the ultrasonic echo signal processing circuit processes the received ultrasonic signals, and the online temperature measuring circuit measures the liquid temperature. The device generates a 1Mhz sine wave signal through an ultrasonic signal generator circuit, drives an ultrasonic transducer to generate ultrasonic waves, the ultrasonic waves are received by the transducer at the other end and then are filtered and amplified, analog signals are converted into digital signals, a data processing unit processes ultrasonic echo signals, the propagation time of the ultrasonic waves is calculated, temperature signals are received, the propagation time of the ultrasonic waves in liquid is combined with the temperature of the liquid to perform data calculation and analysis, and the concentration of the liquid is calculated.
Description
Technical Field
The invention belongs to the field of ultrasonic precision measurement, and particularly relates to a device and a method for precisely measuring liquid concentration based on SOPC.
Background
Ultrasonic waves are used in many applications in industrial testing. The chemical composition, concentration and density of many measured media (such as chemical solution, suspension, emulsion, and solid-liquid two-phase solution containing small particles) can be measured by measuring the propagation velocity, attenuation, scattering, acoustic impedance, and the like of ultrasonic waves. The most used and most effective measurement method among them is the sound velocity method. The instrument determines the concentration of a measured medium by measuring the sound velocity and the temperature by utilizing the principle that each medium has fixed sound velocity under certain state conditions (concentration and temperature) and the sound velocity of the medium is changed when the concentration and the temperature of the medium are changed.
In practical applications, since the sound velocity is calculated by measuring the propagation time t (i.e. sound time) of the ultrasonic wave on a fixed sound path L, for simplicity, we do not directly use the relationship among sound velocity, temperature and concentration to measure the concentration, but directly consider the relationship among temperature, concentration and sound time, and obtain the relationship curve among temperature, concentration and sound time by measuring in advance:
n＝f(T，t)
wherein n represents concentration, T represents temperature, and T represents sound. This relationship is loaded into a data processor, which then calculates the concentration from the stored relationship based on the temperature measured at the time of actual measurement.
Disclosure of Invention
According to the physical phenomenon that the propagation speeds of ultrasonic waves in the same medium are different at different temperatures, when the ultrasonic waves propagate through the measured medium in the container, the nanosecond ultrasonic wave transmission time measurement is realized on the premise of ensuring the measurement real-time property, and the high-precision liquid concentration measurement can be realized.
The purpose of the invention is realized by the following technical scheme:
the ultrasonic transducer group adopts a plurality of pairs of groups as measuring heads, and two ultrasonic transducers of each pair of groups are oppositely arranged on the outer wall of a container or a pipe wall with larger size and filled with a measured medium in a pairwise way and are not contacted with the measured medium. One of the ultrasonic transducers in each group is used for transmitting ultrasonic waves and one is used for receiving the ultrasonic waves, all the transducers used for transmitting the ultrasonic waves in all the groups of the ultrasonic transducers form a transmitting transducer group, and the transducers used for receiving the ultrasonic waves form a receiving transducer group. The transducer is a piezoelectric transducer, and can convert an electric signal with certain energy into mechanical vibration and also can convert the mechanical vibration into an electric signal. When the frequency of the signal is within the frequency range of the ultrasonic wave, the ultrasonic transducer converts the electrical signal into an ultrasonic signal, and when the ultrasonic signal is applied to the transducer, the transducer converts the ultrasonic signal into an electrical signal, which may be referred to as an ultrasonic echo signal.
The circuit part mainly comprises an ultrasonic signal generating circuit, an ultrasonic echo signal processing circuit and an online temperature measuring circuit.
The ultrasonic signal generating circuit comprises a digital/analog signal conversion circuit and a power amplifying circuit. The digital/analog signal conversion circuit is used for converting a digital sinusoidal signal sent by the SOPC-based processor into an analog sinusoidal signal, and the power amplification circuit is used for amplifying the power of the sinusoidal signal so that the sinusoidal signal has enough energy to drive the transducers in the ultrasonic transmitting transducer group.
The signal processing circuit mainly comprises a signal filtering circuit, a signal amplifying circuit, an analog/digital signal conversion circuit and a processor (SOPC). The main functions are two: the first function is to generate digital sine signal under the control of CPU, the signal is converted into analog signal by the digital/analog signal conversion circuit, and the analog signal is amplified by the power amplification circuit to drive the transducers in the ultrasonic transducer group. The second function is to complete the sampling of the ultrasonic echo signal and store the data in the storage area inside the FPGA, i.e. the analog signal of the ultrasonic echo is converted into a digital signal by an analog/digital signal converter and is input into the FPGA.
The FPGA simultaneously samples an output sine wave driving signal and an input ultrasonic echo signal and stores the sampled data in a memory; the SOPC processor unit reads sampling data from the FPGA memory of the FPGA, and precisely calculates the corresponding moment of the ultrasonic wave propagation time end point through a subdivision interpolation algorithm; then, the time corresponding to the starting point of the ultrasonic wave propagation time is determined according to the output sine wave driving signal, so that the transmission time of the ultrasonic wave between two transducers which are oppositely arranged is accurately determined, and the liquid concentration of a user is calculated on the basis of the relation among the temperature, the concentration and the propagation time during the ultrasonic wave transmission by utilizing the liquid temperature output by the temperature sensor in real time.
The working principle of the invention is as follows: the ultrasonic wave driving circuit sends out a certain number of periodic sinusoidal signals, the signals can excite the transducers in the ultrasonic wave transducer group to generate ultrasonic waves after acting on the transducers in the ultrasonic wave transducer group, after the ultrasonic wave signals propagate in a medium and reach the transducers corresponding to the ultrasonic wave transducer group, the transducers corresponding to the ultrasonic wave transducer group in the ultrasonic wave transducer group are excited to generate ultrasonic wave echo signals, the amplitude of the echo signals is gradually increased along with the continuous excitation of the ultrasonic wave signals received by the transducers, when the excitation signals stop, the mechanical vibration of the transducers can be continuously and gradually attenuated under the action of inertia, and the amplitude of the echo signals is also gradually reduced, so that the ultrasonic wave echo signals are amplitude-variable periodic signals, and the period of the amplitude-variable periodic signals corresponds to the period of the ultrasonic wave signals. The period during which the amplitude of the echo signal is at a maximum corresponds to the period of the last emitted ultrasonic signal by a transducer of the ultrasonic transducer group.
The propagation time of the ultrasonic wave is the time interval between any point on the ultrasonic signal emitted by the transducer in the transducer group and the corresponding point on the echo signal received by the corresponding transducer in the transducer group. The key to the ultrasonic transit time measurement is to determine the start and end points of the transit time. The start point of the propagation time may be a time corresponding to a particular point on the ultrasonic signal emitted by the transducer, and the end point of the propagation time may be a time corresponding to a point on the echo signal corresponding to a characteristic point of the ultrasonic signal.
The echo signal is a periodic signal of varying amplitude, and the most characteristic wave in the waveform is the wave with the largest amplitude, which can be called the characteristic wave, and the characteristic wave corresponds to the last wave of the ultrasonic signal. In the characteristic wave, the most characteristic points are a zero-crossing point and a peak point, and the zero-crossing point can be selected as the characteristic point of the echo signal. The time corresponding to the characteristic point is the end point of the propagation time, and correspondingly, the time corresponding to the zero-crossing point of the last wave in the ultrasonic wave signal waveform can be determined as the starting point of the propagation time.
Since the ultrasonic signal is generated under the control of the CPU constructed by the FPGA, the starting point of the propagation time, i.e., the time corresponding to the zero-crossing point of the last wave of the ultrasonic signal, is easily determined accurately by the CPU, and the accuracy thereof depends on the operating frequency of the FPGA.
The end point of the propagation time, that is, the time corresponding to the zero-crossing point in the echo signal characteristic wave is determined by a subdivision interpolation algorithm. Firstly, determining the waveform in the period with the maximum peak amplitude value in the echo signal by a subdivision interpolation algorithm according to the analog/digital signal converter sampling signal of the ultrasonic echo stored in the FPGA; then determining the corresponding time of two sampling points (one is larger than zero and the other is smaller than zero) before and after the zero crossing point; and finally, taking two sampling points before and after the zero crossing point as a reference, carrying out subdivision interpolation on the sampling points by using a fitting method, and determining the moment corresponding to the zero crossing point of the echo signal, namely the moment corresponding to the ultrasonic wave propagation time end point, wherein the precision mainly depends on the resolution of analog/digital signal sampling.
The working process of the device and the method for precisely measuring the concentration of the liquid based on the SOPC is as follows:
the transducers in the ultrasonic transducer group E1 and the transducers in the ultrasonic transducer group E2 are oppositely arranged on the outer wall or the pipe wall of a container filled with a measured medium in pairs, a processor unit constructed in the FPGA controls a field programmable gate array FPGA to output a sine wave driving signal, the signal is enabled to sequentially pass through a digital/analog signal conversion circuit and a power amplification circuit, the driving signal is enabled to emit and drive one transducer in the transducer group E1, and the transducer is enabled to convert an input signal into mechanical vibration to generate ultrasonic waves.
The ultrasonic wave receiving transducer group and the corresponding transducer thereof receive the ultrasonic wave signals sent by the transducers in the ultrasonic wave transmitting transducer group and output ultrasonic wave echo signals, the signal filter circuit filters the ultrasonic wave echo signals sent by the transducers in the ultrasonic wave receiving transducer group, the amplifying circuit amplifies the ultrasonic wave echo signals, the analog/digital signal conversion circuit samples the echo signals, and the sampled data is stored in the storage area constructed in the FPGA.
After sampling is finished, the processor unit firstly determines the moment corresponding to the starting point of the ultrasonic wave propagation time according to the data of the ultrasonic wave transmitted by the FPGA, then reads the analog/digital signal sampling data of the ultrasonic wave echo signal from the FPGA, and accurately calculates the moment corresponding to the end point of the ultrasonic wave propagation time by adopting a subdivision interpolation algorithm, thereby accurately determining the transmission time of the ultrasonic wave between two oppositely-installed transducers. The liquid temperature output by the temperature sensor in real time is utilized, and the liquid concentration of a user is calculated based on the relation among the temperature, the concentration and the propagation time during ultrasonic transmission.
The invention adopts a split measuring head which is arranged at the outer side of the measured medium container, ultrasonic waves are transmitted through the measured medium in the container, the transmission time of the ultrasonic waves can be accurately measured, and the measuring head is not contacted with the high-temperature measured medium, thereby reducing the requirement on the material of the measuring head. Meanwhile, a plurality of pairs of measuring heads are uniformly arranged at each position of the measured object, so that the propagation speeds of the ultrasonic waves at a plurality of positions in the liquid are obtained, and the final propagation speed of the ultrasonic waves is calculated through weighted average. By adopting a hardware circuit based on the FPGA and a special software subdivision algorithm, the measurement of the ultrasonic transmission time can reach nanosecond precision, so that the high-precision temperature measurement of the liquid concentration is realized, and good real-time performance can be ensured.
Drawings
FIG. 1 is a schematic view of an installation of an ultrasonic transducer array;
FIG. 2 is a block diagram of an apparatus for precise measurement of liquid concentration based on SOPC;
FIG. 3 is a schematic diagram of the drive signals applied to the ultrasonic transducer group E1 (E11, E12, E13, E14);
FIG. 4 is a schematic diagram of ultrasonic echo signals received at the ultrasonic transducer group E2 (E21, E22, E23, E24);
FIG. 5 is a schematic diagram of the hardware operation principle of a method for precisely measuring the transmission time of ultrasonic waves;
fig. 6a-6b are schematic diagrams of the time instants corresponding to the end points of the ultrasonic propagation time.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Referring to fig. 1, a schematic structural diagram of a split type four-channel liquid concentration measuring device is shown. Four pairs of ultrasonic transducers (E11 and E21, E12 and E22, E13 and E23, and E14 and E24) are respectively installed on the outer wall of the cylindrical container containing the medium to be measured, and are positioned at a position lower than the height of the medium to be measured, so that ultrasonic waves can penetrate through the medium to be measured. Wherein the transducers E11, E12, E13, E14 are used for transmitting ultrasonic signals and the transducers E21, E22, E23, E24 are used for receiving ultrasonic echo signals. Fig. 1 (a) is a plan view showing the installation of the ultrasonic transducer group, and fig. 1 (b) is a front view showing the installation of the ultrasonic transducer group.
Referring to fig. 2, the invention mainly comprises an ultrasonic transmitting transducer group, an ultrasonic receiving transducer group, a field programmable gate array FPGA, a processor unit constructed based on the FPGA, an analog/digital signal conversion circuit, an amplifying circuit, a filter circuit, a power amplifying circuit, and a digital/analog conversion circuit.
Referring to fig. 3, the driving signal is applied to the transducers in the ultrasonic transmitting transducer group, and is formed by converting a digital sinusoidal signal generated in an FPGA into an analog sinusoidal signal through a D/a conversion circuit and then amplifying the analog sinusoidal signal through a power amplification circuit, wherein V in the figure represents the voltage of the signal and t represents time. The signal has a frequency of 1MHz, a voltage of about 10V, a current of about 1.5A, and a power of about 15 watts, which is sufficient to drive the transducers in the ultrasonic transducer array to convert the power into mechanical power and emit an ultrasonic signal.
Referring to fig. 4, the ultrasonic echo signals output from the transducers in the ultrasonic receiving transducer group are shown, wherein V represents the voltage of the signal and t represents time. When the ultrasonic signals sent by the transducers in the transducer group E1 are transmitted to the transducers in the transducer group after a certain transmission time, the transducers in the receiving transducer group convert the mechanical energy of the ultrasonic signals into electric energy and output ultrasonic echo signals. The amplitude of the electric signal output by the transducer in the receiving transducer group is zero before the ultrasonic wave is not transmitted to the transducer in the receiving transducer group, after the transducer in the receiving transducer group receives the ultrasonic wave signal, the amplitude of the output electric signal is gradually increased and then gradually reduced and attenuated to zero, the electric signal is a variable amplitude periodic signal, and the wave with the maximum amplitude corresponds to the last wave of the ultrasonic wave signal. The frequency of the ultrasonic echo signal depends on the frequency of the ultrasonic signal, which is also 1MHz.
Referring to fig. 5, after the CPU processing unit built in the FPGA sends a start sampling command to the synchronization circuit in the FPGA, the FPGA starts driving the transducers in the ultrasonic wave transmitting transducer group and sampling output signals of the transducers in the ultrasonic wave receiving transducer group.
A digital sinusoidal signal generator 431 constructed in the FPGA sends 8 cycles of sinusoidal signals with a frequency of 1MHz, the signals are converted into analog signals through a digital/analog model conversion circuit 14, and the analog signals are amplified through a power amplification circuit and loaded on one transducer in the transmitting transducer group to send out ultrasonic signals. The electric signals output by the transducers in the receiving transducer group are filtered by the filter circuit, amplified by the operational amplifier circuit and then connected to the analog/digital signal conversion circuit. And a sampling circuit in the FPGA controls the analog/digital signal conversion circuit to convert the analog signals into digital signals, and the sampling values are stored in an RAM storage area built in the FPGA one by one. After sampling is finished, the FPGA sends sampling end state information to the CPU processing unit, and the CPU processing unit finishes one-time sampling after receiving the sampling end state information.
After sampling is finished, the CPU processing unit firstly accurately determines the time T corresponding to the starting point in the ultrasonic signal according to the data of the digital sine signal generator in the FPGA QD 。
Then the CPU sends out a data reading command, reads the data temporarily stored in the RAM storage area, and accurately calculates the time corresponding to the ultrasonic wave propagation time end point.
The time corresponding to the ultrasonic transmission time end point is realized by analyzing and calculating all sampling data of the echo signal by using a subdivision interpolation algorithm. Referring to fig. 6a, analyzing the ultrasonic echo signals output by the transducers in the ultrasonic receiving transducer group, to ensure the repeatability of the measurement, the endpoint of the ultrasonic wave transmission time should be extracted from the waveform with the maximum peak amplitude. The most obvious two characteristic points are a peak point and a zero-crossing point in the whole period of the waveform, and the high precision is easier to obtain by determining the zero-crossing point as a time reference point of the echo signal.
Referring to fig. 6a, the method for calculating the time corresponding to the ultrasonic transmission time end point of the present invention is:
firstly, comparing analog/digital signal sampling points point by point, finding out the maximum value of the sampling points, and then easily determining the waveform with the maximum amplitude value, wherein the waveform can be called as a characteristic value waveform;
next, referring to FIG. 6b, the zero crossing point P corresponding to the end point of the ultrasonic transmission time is determined 0 The front sample point P and the rear sample point P 1 Obviously, the sampling value of the sampling point P in the characteristic wave is greater than zero, and the sampling value of the sampling point P1 is less than zero;
finally, with sample points P and P 1 The time corresponding to the two points is used as a reference, and the zero crossing point P can be accurately calculated by using a subdivision interpolation algorithm 0 The corresponding time is calculated by the following specific method:
let the sampling frequency of the analog/digital signal be F A/D The time between two adjacent sampling points, i.e. the sampling period, is T A/D (ii) a The number of samples from the first sampling point to the sampling point P is N, and the sampling value corresponding to the sampling point P is V 1 The time corresponding to the sampling point P is T 1 (ii) a The sampling value corresponding to the sampling point P1 is V 2 (ii) a The time corresponding to the sampling point P is T 1 Sampling point P and zero crossing point P 0 The time between is T 2 Zero crossing point P 0 Corresponding toAt a time T ZD And the transmission time of the ultrasonic wave is T, then:
in a small region near the zero crossing point, the waveform of the sine wave is close to a straight line, and T can be determined according to a straight line interpolation method 2 ：
The time corresponding to the zero crossing point, that is, the time corresponding to the ultrasonic transmission time end point, is:
as can be seen from the above equation, the resolution of the time corresponding to the ultrasonic transmission time end point is:
referring to fig. 6b, assuming that the frequency of the ultrasonic echo signal is 1MHz, the period is 1us; the resolution of the analog/digital signal is 12 bits, the amplitude of the signal can be divided into 4096 parts, and if the sampling frequency of the analog/digital signal is 32MHz, a maximum of 16 points can be taken in a half period from the positive maximum value to the negative maximum value of the sine wave, and if the waveform in the half period from the positive maximum value to the negative maximum value of the sine wave is regarded as a straight line, it is obvious that:
when the waveform of the sine wave in the half period from the positive maximum value to the negative maximum value is observed, the slope of the curve near the zero crossing point is far larger than that of the curve near the peak value, and then
|V 2 -V 1 |＞256
Referring to fig. 6, the transmission time of the ultrasonic wave is:
since the time corresponding to the start point of the ultrasonic transmission time can be accurately determined, the resolution of the ultrasonic transmission time measurement depends on the resolution of the time corresponding to the end point of the ultrasonic transmission time, and thus the resolution of the ultrasonic transmission time measurement is less than 0.122 nanosecond. The distance between a plurality of pairs of two transducers which correspond to each other and are arranged on a cylindrical container is fixed, the propagation time of ultrasonic waves between the two transducers which correspond to each other under different concentrations is measured, the propagation speed of the ultrasonic waves at a plurality of positions in liquid is obtained due to the fixed propagation distance of the ultrasonic waves, and the final propagation speed of the ultrasonic waves is calculated through weighted average. By adopting a hardware circuit based on the FPGA and a special software subdivision algorithm, the measurement of the ultrasonic transmission time can reach nanosecond precision, so that the high-precision temperature measurement of the liquid concentration is realized, and the good real-time property can be ensured. For example, the propagation velocity of ultrasonic waves in a sodium chloride solution having a concentration (g/mL) of 0.02 at a temperature of 12.15 ℃ is 1354.321m/s, the propagation velocity of ultrasonic waves is 1390.871m/s when the concentration (g/mL) of the sodium chloride solution is 0.04, and the propagation velocity of ultrasonic waves is 1468.527m/s when the concentration (g/mL) of the sodium chloride solution is 0.08. The wave velocity of the ultrasonic wave in the sodium chloride solution monotonically increases along with the increase of the solution concentration, and the wave velocity and the solution concentration in the sodium chloride solution have a good linear relationship: y =1888.27x +1316.58, the concentration of the solution is 0.01g/mL higher per liter in a certain concentration range, and the wave speed of ultrasonic waves in the sodium chloride solution is improved by 18.88m/s. Therefore, under the condition of determining the propagation distance of the ultrasonic wave, the precision measurement of the liquid concentration can be realized by accurately measuring the propagation time of the ultrasonic wave.
Claims (10)
1. A device and a method for precisely measuring liquid concentration based on SOPC comprise an ultrasonic transducer group, an ultrasonic signal generating circuit, an ultrasonic echo signal processing circuit and an online temperature measuring circuit. The method is characterized in that: the ultrasonic wave signal generator circuit generates a 1Mhz sine wave signal, the ultrasonic wave transducer is driven to generate ultrasonic waves, the ultrasonic waves are received by the transducer at the other end, filtered and amplified, analog signals are converted into digital signals, the SOPC-based data processing unit processes ultrasonic wave echo signals, the propagation time of the ultrasonic waves is calculated, meanwhile, the SOPC-based data processing unit also receives temperature signals sent by the online temperature measuring circuit, and the SOPC-based data processing unit combines the propagation time of the ultrasonic waves in liquid with the temperature of the liquid to perform data calculation and analysis, so that the concentration of the liquid is calculated.
2. The device and the method for precisely measuring the concentration of the liquid based on the SOPC as claimed in claim 1, wherein the generation of the ultrasonic digital signals, the processing of the ultrasonic echo digital signals, the implementation of the ultrasonic transmission time measuring algorithm and the calculation of the concentration of the liquid are mainly realized by the SOPC technology.
3. The ultrasonic transducer group of claim 1 adopts a plurality of pairs of groups, as measuring heads, two ultrasonic transducer groups are arranged on the outer wall of the container of the measured medium in pairs, and are not contacted with the measured medium; one of the ultrasonic transducers in each group is used for transmitting ultrasonic waves, the other one is used for receiving the ultrasonic waves, all the transducers in all the ultrasonic transducer groups used for transmitting the ultrasonic waves form a transmitting transducer group E1, the transducers used for receiving the ultrasonic waves form a receiving transducer group E2, and the transducers are uniformly distributed on the pipe wall.
4. The ultrasonic signal generator circuit of claim 1, comprising a digital signal generating circuit, a digital/analog signal converting circuit for converting a digital sinusoidal signal from the SOPC-based processing unit into an analog sinusoidal signal, and a signal power amplifier for amplifying the power of the sinusoidal signal to drive the transducers of the ultrasonic transmitting transducer array.
5. The analog/digital signal conversion circuit according to claim 1, connected to the signal amplification circuit, for converting the signal-filtered ultrasonic echo analog signal into a digital signal and inputting the digital signal to the SOPC-based processor unit.
6. The SOPC-based processor unit of claim 1, outputting a sine wave drive signal, simultaneously sampling the output sine wave drive signal and the input ultrasonic echo signal, storing the sampled data in a memory, reading the sampled data in the memory, and calculating the transmission time of ultrasonic waves between all transducer groups.
7. The on-line temperature measuring device of claim 1, which mainly measures the temperature of the liquid, mainly comprises a temperature sensor and a processing circuit.
8. The SOPC-based processor unit of claim 1, wherein the liquid concentration is calculated by combining the ultrasonic transit time with a liquid temperature parameter.
9. The software algorithm comprises a characteristic wave searching algorithm and a software subdivision interpolation algorithm. The characteristic wave searching algorithm is used for analyzing and comparing the sampling data stored in the RAM memory and finding out the characteristic wave with the maximum amplitude in the echo signal. And analyzing and processing the sampling data of the characteristic wave by a software subdivision interpolation algorithm, and calculating the end point moment of the propagation time.
10. The high-resolution analog/digital signal conversion circuit and the linear interpolation algorithm are adopted, the hardware circuit and the software algorithm are organically combined, the precise measurement of the ultrasonic wave propagation time is guaranteed, meanwhile, the SOPC-based hardware circuit enables data to be rapidly processed, and the concentration measurement has good real-time performance.
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Application publication date: 20221028 |