CN101813528B - Method for precisely measuring temperature by using ultrasonic technology and measuring instrument - Google Patents

Abstract

The invention relates to a method for precisely measuring temperature by using ultrasonic technology and a measuring instrument, mainly composed of an ultrasonic temperature sensor, an ultrasonic transducer drive circuit, an ultrasonic echo signal processing circuit and an interface circuit. The ultrasonic temperature sensor consists of two parts: an ultrasonic transducer and a closed tube filled with a medium capable of propagating ultrasonic waves. The driving circuit of the ultrasonic transducer mainly includes a digital-to-analog converter D/A and a power amplifier circuit. The ultrasonic echo signal processing circuit is mainly composed of filter circuit, amplifier circuit, A/D, FPGA and CPU. The ultrasonic transducer drive circuit drives the transducer to emit ultrasonic waves, and the ultrasonic echo signal processing circuit precisely measures the propagation time of ultrasonic waves in the pipe body. The propagation speed of ultrasonic waves in the medium changes with the change of temperature, and the measurement of temperature can be realized by measuring the propagation time of ultrasonic waves in the pipe body at different temperatures. The thermometer can realize high-precision temperature measurement, the accuracy of temperature measurement depends on the measurement accuracy of ultrasonic propagation time, and the measurement range depends on the length of the pipe body.

Description

A method and measuring instrument for precise temperature measurement using ultrasonic technology

technical field

The invention belongs to the technical field of precision sensors and detection, and in particular relates to a temperature measuring instrument which uses ultrasonic technology to precisely measure temperature.

Background technique

The salient feature of ultrasound is its high frequency, thus its short wavelength, small diffraction phenomenon, good directionality, and directional propagation. When it encounters impurities or interfaces during propagation, there will be significant reflection. With the development of electronic technology, ultrasonic technology is more and more used in precision measurement of temperature and so on.

When ultrasonic waves propagate in a medium, the propagation speed changes with the change of state parameters such as temperature and pressure. When the ultrasonic wave propagates in the gas, the propagation speed is about hundreds of meters per second, and it increases with the increase of temperature. The speed of sound in the air is 331.4 m/s at 0°C, and 340 m/s at 15°C. When the temperature rises by 1°C , the speed of sound increases by about 0.6 m/s. The temperature can be measured by measuring the propagation time of the ultrasonic wave at different temperatures when the transmission distance is constant. For example, the speed of ultrasonic waves at 20°C is 344 m/s, and the speed of ultrasonic waves at 21°C is 344.6 m/s. If the transmission distance of ultrasonic waves is 0.3 meters, the transmission time of ultrasonic waves at 20°C is 8.7209×10 ^-4 seconds, the ultrasonic transmission time at 21°C is 8.7057×10 ^-4 seconds, and the difference between the ultrasonic transmission time at 21°C and 20°C is 1.52×10 ^-6 seconds. To ensure that the measurement reaches a measurement resolution of 0.001°C, it is required that the measurement resolution of the ultrasonic transit time must reach 1 to 2 nanoseconds. If a conventional timing counting circuit is used to measure the transmission time of ultrasonic waves, 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 present invention discloses a precision temperature measurement method and a temperature measuring instrument with a measurement resolution of 0.001°C, and designs an ultrasonic temperature sensor, an FPGA circuit and a software subdivision and interpolation algorithm, which can ensure real-time measurement Under the premise, the measurement of nanosecond ultrasonic transmission time can be realized, so as to realize high-precision temperature measurement.

The technical scheme adopted in the present invention is:

The invention is used to realize precise temperature measurement with a measurement resolution better than 0.001°C. The temperature measurement method adopts two parts: an ultrasonic temperature sensor, a hardware circuit and a related algorithm. The ultrasonic temperature sensor consists of a sealed pressure-resistant tube filled with ultrasonic medium and two ultrasonic transducers E1 and E2 respectively installed at both ends of the tube; the hardware circuit mainly includes an ultrasonic transducer drive circuit, an ultrasonic echo signal filter circuit, Amplifying circuit and signal processing circuit. Signal processing circuits mainly include analog-to-digital converter (A/D), field programmable gate array (FPGA) and central processing unit (CPU).

The transducer E1 is a piezoelectric sensor that can convert electrical signals with certain energy into mechanical vibrations. When the frequency of the signals is within the frequency range of ultrasonic waves, the transducer E1 converts electrical signals into ultrasonic signals. Transducer E2 is also a piezoelectric sensor that converts mechanical vibrations into electrical signals. When the ultrasonic signal acts on the ultrasonic transducer E2, it converts the ultrasonic signal into an electrical signal. This signal can be called an ultrasonic echo signal. .

The ultrasonic transducer drive circuit includes a digital-to-analog converter (D/A) and a power amplifier 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 E1. The A/D converter is mainly used to convert the ultrasonic echo analog signal into a digital signal and input it into FPGA.

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, which is converted into an analog signal by a D/A converter and amplified by a power amplifier circuit to drive the transducer E1 . 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 E1 emits a certain amount of periodic sinusoidal ultrasonic signals. After the signal propagates in the medium and reaches transducer E2, it excites transducer E2 to generate an ultrasonic echo signal. The amplitude of the echo signal varies with the transducer E2. 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 emitted by the transducer E1 last.

The ultrasonic propagation time is the time interval between any point on the ultrasonic signal sent by the transducer E1 and the corresponding point on the echo signal received by the transducer E2. 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 specific point on the ultrasonic signal sent by the transducer E1, and the end point of the time may be 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 and interpolated by the fitting method to determine the time corresponding to the echo signal zero-crossing point, that is, the ultrasonic The accuracy of the moment corresponding to the end of the propagation time depends mainly on the resolution of the A/D sampling.

The high-precision ultrasonic temperature measurement method proposed by the present invention is as follows: the ultrasonic transducer E1 and the ultrasonic transducer E2 are relatively installed at both ends of the pipe body, and the central processing unit CPU controls the field programmable gate array FPGA to output the sine wave drive signal, so that the signal The input signal is sequentially input to the ultrasonic transducer E1 through a D/A conversion circuit and a power amplifier circuit, and the ultrasonic transducer E1 converts the input signal into a mechanical vibration to generate an ultrasonic signal.

The ultrasonic transducer E2 receives the ultrasonic signal sent by the ultrasonic transducer E1, and outputs an ultrasonic echo signal, the ultrasonic echo signal sent by the ultrasonic transducer E2 is filtered by the filter circuit, and then the ultrasonic echo signal is filtered by the amplifier circuit. After amplification, the echo signal is sampled by the A/D conversion circuit, and the sampled data is first stored in the storage area constructed in the FPGA.

After the sampling is completed, the central processing unit CPU first determines the time corresponding to the starting point of the ultrasonic propagation time according to the data transmitted by the FPGA, and then reads the A/D sampling data of the ultrasonic echo signal from the FPGA, and uses the subdivision interpolation algorithm to accurately Calculate the moment corresponding to the end point of the ultrasonic propagation time, and then accurately determine the propagation time of the ultrasonic wave between the two transducers E1 and E2. Finally, the CPU accurately calculates the temperature of the temperature sensor according to the different transmission times of the ultrasonic waves between the two transducers E1 and E2 in the ultrasonic temperature sensor tube, combined with the transmission speed of the ultrasonic waves at different temperatures and in different media.

Thus, the high-precision ultrasonic thermometer proposed by the present invention includes ultrasonic transducer E1, ultrasonic transducer E2, D/A conversion circuit, power amplifier circuit, signal amplifier circuit, filter circuit, A/D conversion circuit, field programmable Gate array FPGA and central processing unit CPU;

The ultrasonic transducer E1 and the ultrasonic transducer E2 are installed oppositely at both ends of the pipe body, and there is a medium capable of propagating ultrasonic waves between the two transducers.

Described central processing unit CPU connects Field Programmable Gate Array FPGA, controls Field Programmable Gate Array FPGA to output sine wave drive signal, the one output of Field Programmable Gate Array FPGA connects D/A conversion circuit, by D/A conversion circuit The sine wave drive signal is converted, and 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 E1, and the signal is input to the ultrasonic transducer E1. The transducer E1 converts the input signal into a mechanical vibration to generate an ultrasonic signal;

The ultrasonic transducer E2 receives the ultrasonic signal sent by the ultrasonic transducer E1, 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, and accurately calculates the time corresponding to the end point of the ultrasonic propagation time through a subdivision interpolation algorithm; then, determines the ultrasonic propagation time according to the output sine wave drive signal The moment corresponding to the origin of time. Thus, the transmission time of the ultrasonic waves between the two transducers E1, E2 can be precisely determined. Finally, the CPU accurately calculates the temperature of the temperature sensor according to the different transmission times of the ultrasonic waves between the two transducers E1 and E2 in the ultrasonic temperature sensor tube, combined with the transmission speed of the ultrasonic waves at different temperatures and in different media.

Due to the adoption of the FPGA-based hardware circuit and special software subdivision algorithm, the present invention can realize the measurement of ultrasonic transmission time with nanosecond precision, thereby realizing high-precision temperature measurement with a resolution better than 0.001°C, and ensuring a good real-time. The invention can be widely used in the fields of precise temperature measurement and control and the like.

Description of drawings

Figure 1 is a structural diagram of a high-precision thermometer;

Fig. 2 is a schematic diagram of a drive signal applied to the transducer E1;

Fig. 3 is a schematic diagram of the ultrasonic echo signal received on the transducer E2;

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 present invention will be described in further detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, this thermometer mainly consists of tube body 10, ultrasonic transducer E111, transducer E212, central processing unit CPU19, field programmable gate array FPGA118, A/D conversion circuit 17, filter circuit 16, amplifying circuit 15 , The power amplifier circuit 14, the D/A conversion circuit 13, the display circuit 20, the keyboard circuit 21 and the D/A conversion circuit 22 constitute. The tube body 10 and the ultrasonic transducers E111 and E212 at both ends of the tube form a temperature sensor. The tube body is filled with a medium that can transmit ultrasonic waves and whose velocity is greatly affected by temperature, such as air and water. The display circuit 20 is used to display the temperature value calculated by the CPU, the keyboard circuit 21 is used to input the parameters of the thermometer and the authority of the operator, and the D/A conversion circuit 22 converts the temperature value from a digital signal to an analog current signal, and outputs an engineering control signal. Commonly used in the 4 ~ 20 mA standard current signal. Ultrasonic transducers are piezoelectric sensors.

See Figure 2, it is the drive signal on the ultrasonic transducer E1, 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 voltage is about 10V, the current is about 1.5A, and it has about 15 watts of electric energy, which is enough to drive the ultrasonic transducer E1 to convert the electric energy into mechanical energy and send out an ultrasonic signal.

Referring to Fig. 3, it is the ultrasonic echo signal output on the transducer E2, V in the figure represents the voltage of the signal, and t represents the time. When the ultrasonic signal sent by the transducer E1 propagates to the transducer E2 after a certain propagation time, the transducer E2 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 E2, the amplitude of the electric signal output by the transducer E2 is zero. After the transducer E2 receives the ultrasonic signal, the amplitude of the electric signal output gradually increases, 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 E111 and sampling the output signal of the ultrasonic transducer E212 .

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 E111, an ultrasonic signal is sent out. The electrical signal output by the transducer E212 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, analyzing the ultrasonic echo signal output by the ultrasonic transducer E2 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 invention 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:

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

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">T</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}$

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:

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}$

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

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; ZD</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">T</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}$

It can be seen from the above formula that the resolution of the time corresponding to the end point of ultrasonic transmission time is:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}$

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:

$\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4096</span>}}{\mathrm{<span\; class="notranslate">\; 16</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 256</span>}$

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

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 256</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 256</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 32</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&mu;s</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.122</span>}\mathrm{<span\; class="notranslate">\; ns</span>}$

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

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; ZD</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; QD</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; D.</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="V"\; filenames="HSA00000109759000023.png"\; state="\{\{state\}\}">V</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; AD</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; QD</span>}}$

Since the time corresponding to the starting point of the ultrasonic transmission time can be accurately determined, the resolution of the measurement of the ultrasonic transmission time depends on the resolution of the time corresponding to the end of the ultrasonic transmission time, and the resolution of the measurement of the ultrasonic transmission time is less than 0.122 nanoseconds. The distance between the transducers E1 and E2 installed at both ends of the pipe body is fixed, according to the measured propagation time of ultrasonic waves between transducers E1 and E2, combined with the speed of ultrasonic waves at different temperatures and in different media, The temperature of the temperature sensor can be calculated. For example, the speed of ultrasonic waves at 20°C is 344 m/s, and the speed of ultrasonic waves at 21°C is 344.6 m/s. If the distance between transducers E1 and E2 is 0.3 meters, the transmission time of ultrasonic waves at 20°C It is 8.7209×10 ^-4 seconds, the transmission time of ultrasonic waves at 21°C is 8.7057×10 ^-4 seconds, and the difference between the transmission times of ultrasonic waves at 21°C and 20°C is 1.52×10 ^-6 seconds. As mentioned above, the measurement resolution of ultrasonic transit time is better than 1.0×10 ⁻⁹ seconds, and the temperature measurement with resolution better than 0.001° C. can be realized.

Claims (4)

1. A method for precision temperature measurement with ultrasonic technology, characterized in that: the method is that ultrasonic transducer E1 and ultrasonic transducer E2 are relatively installed at both ends in a closed pressure-resistant pipe full of ultrasonic medium Constitute an ultrasonic temperature sensor, control field programmable gate array FPGA output sine wave drive signal with central processing unit CPU, allow signal input to described ultrasonic transducer E1 through D/A conversion circuit and power amplification circuit successively, by described The ultrasonic transducer E1 converts the input signal into a mechanical vibration to generate an ultrasonic signal; The ultrasonic transducer E2 receives the ultrasonic signal sent by the ultrasonic transducer E1, and outputs an ultrasonic echo signal, the ultrasonic echo signal sent by the ultrasonic transducer E2 is filtered by the filter circuit, and then the ultrasonic echo signal is filtered by the amplifier circuit. After amplification, the echo signal is sampled by the A/D conversion circuit, and the sampled data is first stored in the storage area constructed in the FPGA; After the sampling is completed, the central processing unit CPU first determines the time corresponding to the starting point of the ultrasonic propagation time according to the data transmitted by the FPGA, and then reads the A/D sampling data of the ultrasonic echo signal from the FPGA, and accurately calculates it through the subdivision interpolation algorithm The moment corresponding to the end point of the ultrasonic propagation time is obtained, and then the ultrasonic transmission time between the two transducers E1 and E2 is accurately determined; The temperature of the temperature sensor can be accurately calculated by combining the different transmission times between different temperatures and the transmission speed of ultrasonic waves in different media; The moment corresponding to the starting point of the sound wave propagation time is the moment corresponding to the zero-crossing point of the last wave of the FPGA transmitting ultrasonic signal; The subdivision and interpolation algorithm of the end point of the calculation propagation time is: according to the A/D sampling signal of the ultrasonic echo stored in the FPGA, at first determine the waveform in the period of the maximum peak amplitude in the echo signal; then determine the The time corresponding to the two sampling points before and after the zero point; finally, based on the two sampling points before and after the zero crossing point, use the fitting method to subdivide the sampling points to determine the time corresponding to the zero point of the echo signal, that is, the ultrasonic propagation time The moment corresponding to the end point. 2. The method for precise temperature measurement using ultrasonic technology according to claim 1, characterized in that: said transducers E1 and E2 are piezoelectric sensors. 3. A high-precision ultrasonic temperature measuring instrument that realizes the method described in claim 1 or 2, is characterized in that: it comprises ultrasonic transducer E1, ultrasonic transducer E2, D/A conversion circuit, power amplifier circuit, signal Amplifying circuit, filtering circuit, A/D conversion circuit, field programmable gate array FPGA and central processing unit CPU; The ultrasonic transducer E1 and the ultrasonic transducer E2 are relatively installed at both ends of a closed pressure-resistant pipe body, and the space between the two transducers is filled with ultrasonic medium; Described central processing unit CPU connects Field Programmable Gate Array FPGA, controls Field Programmable Gate Array FPGA to output sine wave drive signal, the one output of Field Programmable Gate Array FPGA connects D/A conversion circuit, by D/A conversion circuit The sine wave drive signal is converted, and 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 E1, and the signal is input to the ultrasonic transducer E1. The transducer E1 converts the input signal into a mechanical vibration to generate an ultrasonic signal; The ultrasonic transducer E2 receives the ultrasonic signal sent by the ultrasonic transducer E1, 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, and accurately calculates the time corresponding to the end point of the ultrasonic propagation time through a subdivision interpolation algorithm; then, determines the ultrasonic propagation time according to the output sine wave drive signal The moment corresponding to the starting point of time, so as to accurately determine the transmission time of the ultrasonic wave between the two transducers E1, E2; finally, the CPU according to the different transmission time of the ultrasonic wave between the two transducers E1, E2 in the ultrasonic temperature sensor tube Time, combined with the transmission speed of ultrasonic waves at different temperatures and in different media, accurately calculate the temperature of the temperature sensor; The moment corresponding to the starting point of the sound wave propagation time is the moment corresponding to the zero-crossing point of the last wave of the FPGA transmitting ultrasonic signal; The subdivision and interpolation algorithm of the end point of the calculation propagation time is: according to the A/D sampling signal of the ultrasonic echo stored in the FPGA, at first determine the waveform in the period of the maximum peak amplitude in the echo signal; then determine the The time corresponding to the two sampling points before and after the zero point; finally, based on the two sampling points before and after the zero crossing point, use the fitting method to subdivide the sampling points to determine the time corresponding to the zero point of the echo signal, that is, the ultrasonic propagation time The moment corresponding to the end point. 4. The high-precision ultrasonic temperature measuring instrument according to claim 3, characterized in that: the transducers E1 and E2 are piezoelectric sensors.

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