CN201837420U - Device for precisely measuring ultrasonic wave transmission time - Google Patents

Abstract

The utility model relates to a device for precise measurement of ultrasonic transmission time, which adopts two ultrasonic transducers A and B, a hardware circuit and a software subdivision algorithm. The hardware circuit mainly includes an ultrasonic transducer driving circuit, an ultrasonic echo signal filtering circuit, an amplifying circuit and a signal processing circuit. Signal processing circuits include analog-to-digital converters, FPGAs, and CPUs. The CPU controls the FPGA to start the ultrasonic transducer driving circuit to drive transducer A to send out ultrasonic signals, and the filter circuit filters the ultrasonic echo signals received by ultrasonic transducer B, and after amplification, A/D samples the echo signals , the sampling data is first stored in the storage area constructed in the FPGA. After the sampling is completed, the CPU reads the sampling data from the FPGA, and uses the software subdivision algorithm to accurately calculate the transmission time of the ultrasonic wave between the two transducers A and B. . Due to the adoption of FPGA-based hardware circuit and special software subdivision algorithm, the device can realize the measurement of ultrasonic transmission time with nanosecond precision and ensure good real-time performance.

Description

A device for precise measurement of ultrasonic transmission time

technical field

The utility model belongs to the technical field of precision sensors and detection, in particular to a precision measurement technology of ultrasonic transmission time.

Background technique

The salient features of ultrasonic waves are high frequency, thus short wavelength, small diffraction phenomenon, good directionality, and directional propagation. In liquids and solids, the attenuation is small and the penetrating ability is strong. When encountering impurities or interfaces, there will be significant reflection. With the development of electronic technology, ultrasonic technology is more and more used in the precise measurement of distance and flow.

When the ultrasonic wave propagates in the fluid, the time difference between the forward flow direction and the reverse flow direction is different. For example, the propagation speed of ultrasonic waves in clean water is about 1450m/s. Under the conditions of pipe diameter D=300mm and fluid velocity v=1.33m/s, the time difference between forward and reverse flow is about 1 microsecond, and the measurement must be guaranteed to reach 0.5%. The measurement accuracy requires that the resolution of the measured time difference should reach 1 to 2 nanoseconds, and the measurement resolution of forward and countercurrent propagation time should also be in nanoseconds, or even picoseconds. If a conventional timing and counting circuit is used, the frequency of the clock circuit must reach at least 1G, which is obviously difficult to achieve in terms of instrument development.

Contents of the invention

Aiming at the above problems, the utility model discloses a method and device for precisely measuring the transmission time of ultrasonic waves. Using FPGA circuit and software subdivision and interpolation algorithm, it can realize nanosecond level or even picosecond level under the premise of ensuring real-time measurement. Measurement.

The technical scheme that the utility model adopts is:

The device proposed by the utility model includes ultrasonic transducer A, ultrasonic transducer B, power amplifier circuit, amplifier circuit, filter circuit, A/D conversion circuit, D/A conversion circuit, field programmable gate array FPGA and central processing Unit CPU;

The ultrasonic transducer A is arranged opposite to the ultrasonic transducer B at a certain distance, and there is a medium capable of propagating ultrasonic waves between the two transducers;

The central processing unit CPU is connected to a field programmable gate array FPGA to control the field programmable gate array FPGA to output a sine wave drive signal, and one output of the field programmable gate array FPGA is connected to a D/A conversion circuit, and is passed through the D/A conversion circuit The sine wave drive signal is converted, the D/A conversion circuit is connected to the power amplifier circuit to amplify the signal, the power amplifier circuit is connected to the ultrasonic transducer A, and the signal is input to the ultrasonic transducer A, the The ultrasonic transducer A converts the input signal into a mechanical vibration to generate an ultrasonic signal;

The ultrasonic transducer B receives the ultrasonic signal sent by the ultrasonic transducer A, converts the mechanical vibration into an electrical signal, outputs an ultrasonic echo signal, and passes through the amplification circuit, filter circuit and A/D conversion connected in sequence with it. A circuit, so that the ultrasonic echo signal is sequentially amplified, filtered and A/D converted and then input to the Field Programmable Gate Array FPGA;

The field programmable gate array FPGA simultaneously samples the output sine wave drive signal and the input ultrasonic echo signal, and stores the sampling data in the memory;

The central processing unit CPU reads the sampling data from the field programmable gate array FPGA memory, determines the corresponding moment of the ultrasonic propagation time starting point according to the output sine wave driving signal, and adopts subdivision and interpolation according to the input ultrasonic echo signal. The complementary algorithm accurately calculates the moment corresponding to the end point of the ultrasonic propagation time, and then accurately calculates the transmission time of the ultrasonic wave between the ultrasonic transducer A and the ultrasonic transducer B.

The transducer A is a piezoelectric sensor that can convert electrical signals with certain energy into mechanical vibrations. When the frequency of the signal is within the frequency range of ultrasonic waves, the transducer A converts the electrical signals into ultrasonic signals. Transducer B is also a piezoelectric sensor that converts mechanical vibrations into electrical signals. When the ultrasonic signal is applied to ultrasonic transducer B, it converts the ultrasonic signal into an electrical signal. This signal can be called an ultrasonic echo signal. .

The driving circuit of the ultrasonic transducer includes a digital-to-analog conversion (D/A) and a power amplification circuit. The D/A converter is used to convert the digital sinusoidal signal sent by the FPGA into an analog sinusoidal signal, and the power amplifier circuit is used to amplify the power of the sinusoidal signal so that it has enough energy to drive the ultrasonic transducer A. The A/D converter is mainly used to convert the analog signal of the ultrasonic echo into a digital signal, and the number of digits and the sampling frequency of the A/D converter are important factors affecting the measurement accuracy of the ultrasonic transmission time.

There are two main functions of the FPGA circuit, the first function is to generate a digital sine signal under the control of the CPU, and the second function is to complete the sampling of the ultrasonic echo signal, and store the data in the storage area inside the FPGA .

Ultrasonic transducer A emits a certain amount of periodic sinusoidal ultrasonic signals. After the signal propagates in the medium and reaches transducer B, it excites transducer B to generate an ultrasonic echo signal. The amplitude of the echo signal varies with the transducer The continuous excitation of the received ultrasonic signal increases gradually. When the excitation signal stops, the mechanical vibration of the transducer will continue and gradually attenuate under the action of inertia, and the amplitude of the echo signal will also gradually decrease. Therefore, the ultrasonic The echo signal is a periodic signal with variable amplitude, and its period corresponds to the period of the ultrasonic signal. The period with the maximum amplitude of the echo signal corresponds to the period of the ultrasonic signal sent by the transducer A last.

The ultrasonic propagation time is the time interval between any point on the ultrasonic signal sent by transducer A and the corresponding point on the echo signal received by transducer B. The key to ultrasonic transit time measurement is to determine the start and end of transit time. The starting point of the propagation time may be the moment corresponding to a certain point on the ultrasonic signal sent by the transducer A, and the end point of the time is the moment corresponding to the point corresponding to the characteristic point of the ultrasonic signal on the echo signal.

The echo signal is a periodic signal with variable amplitude. The most characteristic wave in its waveform is the wave with the largest amplitude, which can be called the characteristic wave. The characteristic wave corresponds to the last wave of the ultrasonic signal. In the characteristic wave, the most characteristic points are the zero-crossing point and the peak point, and the zero-crossing point can be selected as the characteristic point of the echo signal. The moment corresponding to the feature point is the end of the propagation time, and correspondingly, the moment corresponding to the zero-crossing point of the last wave in the ultrasonic signal waveform can be determined as the starting point of the propagation time.

Since the ultrasonic signal is generated by the FPGA under the control of the CPU, the starting point of the propagation time, that is, the moment corresponding to the zero-crossing point of the last wave of the ultrasonic signal is easily determined by the CPU, and its accuracy depends on the operating frequency of the FPGA.

The end point of the propagation time, that is, the moment corresponding to the zero-crossing point in the characteristic wave of the echo signal, is determined by a subdivision interpolation algorithm. The subdivision interpolation algorithm first determines the waveform in the cycle with the largest peak amplitude in the echo signal according to the A/D sampling signal of the ultrasonic echo stored in the FPGA; then determines two sampling points before and after the zero crossing point (one is larger than zero , one smaller than zero) corresponds to the moment; finally, based on the two sampling points before and after the zero crossing point, the sampling points are subdivided by the fitting method to determine the time corresponding to the echo signal zero crossing point, that is, the ultrasonic propagation time The accuracy of the moment corresponding to the end point mainly depends on the resolution of A/D sampling.

Because the utility model adopts FPGA-based hardware circuit and special software subdivision algorithm, it can realize the measurement of ultrasonic transmission time with nanosecond precision and ensure good real-time performance. The utility model can be widely used in fields such as realizing flow rate and distance precision measurement by adopting ultrasonic technology.

Description of drawings

Fig. 1 is a hardware structure block diagram of a method for precision measurement of ultrasonic transit time;

Fig. 2 is the schematic diagram of the driving signal added on the transducer A;

Fig. 3 is a schematic diagram of the ultrasonic echo signal received on the transducer B;

Fig. 4 is a schematic diagram of the hardware working principle of a method for precisely measuring ultrasonic transit time;

5a-5b are schematic diagrams for determining the time corresponding to the end point of ultrasonic propagation time.

Detailed ways

The technical solution of the utility model will be described in further detail below in conjunction with the accompanying drawings of the description.

Referring to Fig. 1, the hardware circuit of this method is mainly by ultrasonic transducer A 11, transducer B 12, central processing unit CPU 19, field programmable gate array FPGA 18, A/D conversion circuit 17, filter circuit 16, An amplifier circuit 15, a power amplifier circuit 14, and a D/A conversion circuit are formed. Ultrasonic transducer A 11 and transducer B 12 are placed on the same straight line at a certain distance, and there is a medium that can transmit ultrasonic waves between the two transducers, such as air, water, steel, etc. Ultrasonic transducers are piezoelectric sensors.

See Figure 2, it is the driving signal on the ultrasonic transducer A, which is a digital sinusoidal signal generated in the FPGA, which is converted into an analog sinusoidal signal by a D/A conversion circuit, and then amplified by a power amplifier circuit. V represents the voltage of the signal, and t represents time. The frequency of this signal is 1MHz, the maximum voltage is about 10V, the maximum current is about 1.5A, and it has about 15 watts of electrical energy, which is enough to drive the ultrasonic transducer A to convert electrical energy into mechanical energy and send out an ultrasonic signal.

Referring to Fig. 3, it is the ultrasonic echo signal output on the transducer B, V in the figure represents the voltage of the signal, and t represents the time. When the ultrasonic signal from transducer A propagates to transducer B after a certain propagation time, transducer B converts the mechanical energy of the ultrasonic signal into electrical energy and outputs an ultrasonic echo signal. Before the ultrasonic wave propagates to the transducer B, the amplitude of the electrical signal output by transducer B is zero. After the transducer B receives the ultrasonic signal, the amplitude of the output electrical signal increases gradually, and then gradually decreases and attenuates to Zero, is a periodic signal with variable amplitude, and the wave with the largest amplitude corresponds to the last wave of the ultrasonic signal. The frequency of the ultrasonic echo signal depends on the frequency of the ultrasonic signal, which is also 1MHz.

Referring to FIG. 4 , after the CPU 19 sends a start sampling command to the synchronization circuit 432 in the FPGA 18 , the FPGA 18 simultaneously starts driving the ultrasonic transducer A11 and sampling the output signal of the ultrasonic transducer B12 .

The digital sinusoidal signal generator 431 built in the FPGA sends a sinusoidal signal with a frequency of 8 cycles of 1 MHz, which is converted into an analog signal by the D/A conversion circuit 13, and then amplified by the power amplifier circuit 14, and loaded on the transducer On the device A11, an ultrasonic signal is sent out. The electrical signal output by the transducer B12 is amplified by the operational amplifier circuit 15 , filtered by the filter circuit 16 and then connected to the A/D conversion circuit 17 . The sampling circuit 433 inside the FPGA controls the A/D conversion circuit 443 to convert the analog signal into a digital signal, and store the sampled values into the RAM storage area 434 built in the FPGA one by one. After the sampling was completed, the FPGA430 sent the sampling end status information to the CPU 19, and after the CPU 19 received the sampling end status information, it ended a sampling.

After the sampling is finished, the CPU 19 first accurately determines the time T _QD corresponding to the starting point in the ultrasonic signal according to the data of the digital sine signal generator 431 in the FPGA.

Then the CPU 19 issues a read data command, reads the data temporarily stored in the RAM storage area 434, and accurately calculates the time corresponding to the end point of the ultrasonic propagation time.

The moment corresponding to the end point of the ultrasonic transmission time is realized by analyzing and calculating all the sampling data of the echo signal with a subdivision and interpolation algorithm. Referring to Fig. 5a, the analysis of the ultrasonic echo signal output by the ultrasonic transducer B shows that in order to ensure the repeatability of the measurement, the end point of the ultrasonic transmission time should be extracted from the waveform with the largest peak amplitude. In the entire cycle of this waveform, the two most obvious characteristic points are the peak point and the zero crossing point. It is easier to obtain high precision by determining the zero crossing point as the time reference point of the echo signal.

Referring to Fig. 5a, the calculation method of the moment corresponding to the end point of the ultrasonic transmission time of the present utility model is:

First, compare the A/D sampling points point by point, and find out the maximum value of the sampling point to easily determine the waveform with the largest amplitude. This waveform can be called the eigenvalue waveform;

Secondly, referring to Figure 5b, determine the zero-crossing point P ₀ corresponding to the end point of ultrasonic transmission time. The preceding sampling point P and the following sampling point P+1, obviously, the sampling value of sampling point P in the characteristic wave is greater than zero, and sampling point P+ A sample value of 1 is less than zero;

Finally, taking the time corresponding to the sampling point P and P+1 as a benchmark, the time corresponding to the zero-crossing point P ₀ can be accurately calculated by using the subdivision interpolation algorithm. The specific calculation method is as follows:

Let the sampling frequency of A/D be F _A/D , and the time between two adjacent sampling points, that is, the sampling period is T _A/D ; the number of samples from the first sampling point to sampling point P is N, The sampling value corresponding to sampling point P is V1, and the time corresponding to sampling point P is T1; the sampling value corresponding to sampling point P+1 is V2; the time corresponding to sampling point P is T1, and the time between sampling point P and zero crossing point P ₀ The time between is T2, the moment corresponding to the zero crossing point P ₀ is T _ZD , and the transmission time of the ultrasonic wave is T, then:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}$

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}$

In a small area near the zero-crossing point, the waveform of the sine wave is close to a straight line, and T2 can be determined according to the method of linear interpolation:

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}$

Then the moment corresponding to the zero-crossing point, that is, the moment corresponding to the end of the ultrasonic transmission time is:

$T_{\mathrm{ZD}}=T1+T2=N\&times;\frac{1}{f_{A/\mathrm{D.}}}+\frac{1}{V2-V1}\&times;T_{/\mathrm{AD}}\&times;V1$ It can be seen from the above formula that the resolution of the time corresponding to the end point of ultrasonic transmission time is:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}$

Referring to Figure 5b, assuming that the frequency of the ultrasonic echo signal is 1M, the period is 1us; the resolution of the A/D is 12 bits, then the amplitude of the signal can be divided into 4096 parts, and the sampling frequency of the A/D is 32MHz , then within the half period from the positive maximum value to the negative maximum value of the sine wave, a maximum of 16 points can be collected. If the waveform within the half cycle from the positive maximum value to the negative maximum value of the sine wave is regarded as straight line, it is obvious that:

$\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4096</span>}}{\mathrm{<span\; class="notranslate">\; 16</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 256</span>}$

Observing the waveform within half a cycle from the positive maximum value to the negative maximum value of the sine wave, it can be seen that the slope of the curve near the zero crossing point is much larger than the slope of the curve near the peak value, then

V2-V1>256

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 256</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 256</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 32</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&mu;s</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.122</span>}\mathrm{<span\; class="notranslate">\; ns</span>}$

Referring to Figure 5, the transit time of ultrasonic waves is:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; ZD</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; QD</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; QD</span>}}$

Since the moment corresponding to the start point of the ultrasonic transmission time can be accurately determined, the resolution of the measurement of the ultrasonic transit time depends on the resolution of the time corresponding to the end point of the ultrasonic transmission time. The resolution of ultrasonic transit time measurement is less than 0.122 nanoseconds, and if a higher resolution A/D conversion circuit is used, higher resolution measurement can also be realized.

Claims (1)

1. the device in a precisely measuring ultrasonic wave transmission time, described device comprises ultrasonic transducer A, ultrasonic transducer B, power amplification circuit, amplifying circuit, filtering circuit, A/D change-over circuit, D/A change-over circuit, on-site programmable gate array FPGA and central processing unit CPU, it is characterized in that:

Described ultrasonic transducer A and ultrasonic transducer B keep at a certain distance away and are oppositely arranged, exist between two transducers can propagate ultrasound waves medium;

Described central processing unit CPU connects on-site programmable gate array FPGA, control on-site programmable gate array FPGA sine wave output drive signal, one tunnel output of on-site programmable gate array FPGA connects the D/A change-over circuit, by the D/A change-over circuit described sine wave drive signal is changed, the D/A change-over circuit connects power amplification circuit again, signal is amplified, power amplification circuit is connected with ultrasonic transducer A, signal is inputed to described ultrasonic transducer A, and this ultrasonic transducer A converts described this input signal to mechanical vibration and produces ultrasonic signal;

Described ultrasonic transducer B receives the ultrasonic signal that described ultrasonic transducer A sends, mechanical vibration are converted to electric signal, the output ultrasonic wave echoed signal, and by with its amplifying circuit that is connected successively, filtering circuit and A/D change-over circuit, make described ultrasonic echo signal after amplification, filtering and A/D conversion, input to on-site programmable gate array FPGA successively;

Described on-site programmable gate array FPGA sample simultaneously the sine wave drive signal of output and the ultrasonic echo signal of input, and sampled data left in the internal memory.

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