CN101813528B - Method for precisely measuring temperature by using ultrasonic technology and measuring instrument - Google Patents
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Abstract
本发明涉及一种利用超声波技术精密测量温度的方法及测量仪,主要由超声波温度传感器、超声波换能器驱动电路、超声波回波信号处理电路和接口电路组成。超声波温度传感器包括超声波换能器和充满能传播超声波介质的密闭管体两部分。超声波换能器驱动电路主要包括数模转换器D/A和功率放大电路。超声波回波信号处理电路主要由滤波电路、放大电路和A/D、FPGA和CPU组成。超声波换能器驱动电路驱动换能器发出超声波,超声波回波信号处理电路精密测量超声波在管体中的传播时间。超声波在介质中的传播速度随温度的变化而变化,测出超声波在管体中不同温度下的传播时间就可以实现温度的测量。所述温度计可以实现高精度温度测量,温度测量的精度取决于超声波传播时间的测量精度,测量范围取决于管体的长度。
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
技术领域 technical field
本发明属于精密传感器和检测技术领域,具体涉及一种用超声波技术精密测量温度的温度测量仪。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.
背景技术 Background technique
超声波的显著特征是频率高,因而波长短,绕射现象小,方向性好,能够定向传播,传播时遇到杂质或分界面就会有显著的反射。随着电子技术的发展,超声波技术越来越多的应用于温度等的精密测量。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.
超声波在介质中传播时,传播速度随温度、压强等状态参量的变化而变化。超声波在气体中传播时传播速度每秒约数百米,随温度升高而增大,0℃时空气中音速为331.4米/秒,15℃时为340米/秒,温度每升高1℃,音速约增加0.6米/秒。测得传输距离不变时超声波在不同温度下的传播时间,就可以测得温度。例如,20℃时超声波的速度是344米/秒,21℃时超声波的速度是344.6米/秒,如果超声波的传输距离是0.3米,则在20℃时超声波的传输时间是8.7209×10-4秒,在21℃时超声波的传输时间是8.7057×10-4秒,在21℃时和20℃时超声波的传输时间差为1.52×10-6秒。要保证测量达到0.001℃的测量分辨率,要求超声波传输时间测量的分辨率要达到1~2纳秒才能实现。如果用常规的定时计数电路测量超声波的传输时间,则时钟电路的频率至少要达到1G,这对于仪器开发来讲显然很难实现。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.
发明内容 Contents of the invention
本发明针对上述问题,公开了一种测量分辨率可达0.001℃的精密温度测量方法和温度测量仪,设计了超声波温度传感器、FPGA电路和软件细分插补算法,可以在保证测量实时性的前提下实现纳秒级超声波传输时间的测量,从而实现高精度温度测量。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.
本发明采用的技术方案是:The technical scheme adopted in the present invention is:
本发明用于实现测量分辨率优于0.001℃的精密温度测量,所述温度测量方法采用超声波温度传感器、硬件电路及相关算法两部分。超声波温度传感器包括一个充满超声介质的密闭耐压管体和分别安装在管体两端的两个超声波换能器E1和E2;硬件电路主要包括超声波换能器驱动电路、超声波回波信号滤波电路、放大电路和信号处理电路。信号处理电路主要有模数转换器(A/D)、现场可编程门列阵(FPGA)和中央处理单元(CPU)。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).
所述换能器E1是压电式传感器,可以把具有一定能量的电信号转换为机械振动,当信号的频率在超声波的频率范围内时,换能器E1把电信号转换为超声波信号。换能器E2也是压电式传感器,把机械振动转换为电信号,当超声波信号作用到超声波换能器E2上时,它把超声波信号转换为电信号,该信号可以称之为超声波回波信号。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. .
所述超声波换能器驱动电路包括数模转换器(D/A)和功率放大电路。D/A转换器用于把FPGA发出的数字正弦信号转换为模拟正弦信号,功率放大电路用于放大该正弦信号的功率,使之有足够的能量驱动超声波换能器E1。所述A/D转换器主要用于把超声波回波模拟信号转换为数字信号,并输入FPGA。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.
所述FPGA电路主要功能有两个:第一个功能是在CPU的控制下产生数字正弦信号,该信号经D/A转换器转换成模拟信号,并经功率放大电路放大后驱动换能器E1。第二个功能是完成超声波回波信号的采样,并把数据存在构造于FPGA内部的存储区内。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.
超声波换能器E1发射一定数量的周期性正弦超声波信号,该信号在介质中传播到达换能器E2后,激励换能器E2产生超声波回波信号,回波信号的幅值随着换能器接收到的超声波信号的连续激励而逐渐增大,当激励信号停止时,换能器的机械振动在惯性的作用下仍然会持续并逐渐衰减,回波信号的幅值也逐渐减小,因此超声波回波信号是一个变幅周期性信号,其周期对应于超声波信号的周期。回波信号幅值最大的那个周期对应于换能器E1最后发出的那个超声波信号的周期。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.
超声波的传播时间就是换能器E1发出的超声波信号上的任意一点与换能器E2接收到的回波信号上相对应的那一点之间的时间间隔。超声波传输时间测量的关键是确定传播时间的起点和终点。传播时间的起点可以是换能器E1发出的超声波信号上特定所对应的时刻,时间的终点是回波信号上与超声波信号特征点相对应的那一点所对应的时刻。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.
回波信号是一个变幅值周期性信号,其波形中最有特征的波是幅值最大的那个波,可以称之为特征波,特征波对应于超声波信号的最后一个波。在特征波中,最有特征的点是过零点和峰值点,可以选择过零点作为回波信号的特征点。特征点对应的时刻就是传播时间的终点,与之相对应,超声波信号波形中最后那个波的过零点所对应的时刻可以确定为传播时间的起点。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.
由于超声波信号是FPGA在CPU的控制下产生的,传播时间的起点,也就是超声波信号最后那个波的过零点对应的时刻很容易由CPU精确确定,其精度取决于FPGA的运行频率。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.
传播时间的终点,也就是回波信号特征波中过零点所对应的时刻通过细分插补算法来确定。细分插补算法根据FPGA中存储的超声波回波的A/D采样信号首先确定回波信号中峰值幅值最大的那个周期内的波形;然后确定过零点前后两个采样点(一个比零大,一个比零小)所对应的时刻;最后以过零点前后两个采样点为基准,用拟合的方法对采样点进行细分插补,确定回波信号过零点所对应的时刻,即超声波传播时间终点所对应的时刻,其精度主要取决于A/D采样的分辨率。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.
本发明提出的高精度超声波温度测量方法如下:超声波换能器E1与超声波换能器E2相对安装在管体两端,中央处理单元CPU控制现场可编程门阵列FPGA输出正弦波驱动信号,让信号依次通过D/A转换电路和功率放大电路输入至所述超声波换能器E1,该超声波换能器E1将所述该输入信号转换成机械振动产生超声波信号。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.
所述超声波换能器E2接收所述超声波换能器E1发出的超声波信号,并输出超声波回波信号,由滤波电路对超声波换能器E2发出的超声波回波信号进行滤波,再由放大电路进行放大后,由A/D转换电路对回波信号进行采样,采样数据先存储在构造于FPGA内的存储区内。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.
采样完成后,中央处理单元CPU首先根据FPGA发射超声波的数据确定超声波传播时间起点所对应的时刻,然后从FPGA内读取超声波回波信号的A/D采样数据,采用通过细分插补算法精确计算出超声波传播时间终点所对应的时刻,进而精确确定超声波在两个换能器E1、E2之间的传输时间。最后CPU根据超声波在超声波温度传感器管体中两个换能器E1、E2之间的不同传输时间,结合在不同温度下和不同介质中超声波的传输速度,精确计算得到温度传感器的温度。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.
由此,本发明提出的高精度超声波温度计包括超声波换能器E1、超声波换能器E2、D/A转换电路、功率放大电路、信号放大电路、滤波电路、A/D转换电路、现场可编程门阵列FPGA和中央处理单元CPU;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;
所述超声波换能器E1与超声波换能器E2相对安装在管体两端,两个换能器之间存在可以传播超声波的介质。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.
所述中央处理单元CPU连接现场可编程门阵列FPGA,控制现场可编程门阵列FPGA输出正弦波驱动信号,现场可编程门阵列FPGA的一路输出连接D/A转换电路,由D/A转换电路对所述正弦波驱动信号进行转换,D/A转换电路再连接功率放大电路,对信号进行放大,功率放大电路与超声波换能器E1连接,将信号输入至所述超声波换能器E1,该超声波换能器E1将所述该输入信号转换成机械振动产生超声波信号;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;
所述超声波换能器E2接收所述超声波换能器E1发出的超声波信号,把机械振动转换为电信号,输出超声波回波信号,并通过与其依次连接的放大电路、滤波电路和A/D转换电路,使所述超声波回波信号依次经放大、滤波和A/D转换后输入至现场可编程门阵列FPGA;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;
所述现场可编程门阵列FPGA同时采样输出的正弦波驱动信号和输入的超声波回波信号,并将采样数据存放在内存中;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;
所述中央处理单元CPU从现场可编程门阵列FPGA内存中读取采样数据,通过细分插补算法精确计算出超声波传播时间终点所对应的时刻;然后,根据输出的正弦波驱动信号确定超声波传播时间起点所对应的时刻。从而精确确定超声波在两个换能器E1、E2之间的传输时间。最后CPU根据超声波在超声波温度传感器管体中两个换能器E1、E2之间的不同传输时间,结合在不同温度下和不同介质中超声波的传输速度,精确计算得到温度传感器的温度。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.
本发明由于采用了基于FPGA的硬件电路和特殊的软件细分算法,可以实现纳秒级精度的超声波传输时间的测量,从而实现分辨率优于0.001℃的高精度温度测量,并保证很好的实时性。本发明可广泛的用于精密温度测量和控制等领域。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.
附图说明 Description of drawings
图1是一种高精度温度计结构图;Figure 1 is a structural diagram of a high-precision thermometer;
图2是加在换能器E1上的驱动信号示意图;Fig. 2 is a schematic diagram of a drive signal applied to the transducer E1;
图3是换能器E2上接受到的超声波回波信号示意图;Fig. 3 is a schematic diagram of the ultrasonic echo signal received on the transducer E2;
图4是一种精密测量超声波传输时间方法的硬件工作原理示意图;Fig. 4 is a schematic diagram of the hardware working principle of a method for precisely measuring ultrasonic transit time;
图5a-5b是确定超声波传播时间终点所对应时刻的示意图。5a-5b are schematic diagrams for determining the time corresponding to the end point of ultrasonic propagation time.
具体实施方式 Detailed ways
下面结合说明书附图对本发明的技术方案作进一步详细说明。The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings.
参见图1,本温度计主要由管体10、超声波换能器E111、换能器E212,中央处理单元CPU19,现场可编程门列阵FPGE118,A/D转换电路17,滤波电路16,放大电路15,功率放大电路14、D/A转换电路13、显示电路20、键盘电路21和D/A转换电路22构成。管体10和管内两端的超声波换能器E111、超声波换能器E212构成温度传感器,管体中充满可以传播超声波且超声波声速受温度影响较大的介质,比如空气,水等。显示电路20用于显示CPU计算出的温度值,键盘电路21用于向输入温度计的参数及操作人员的权限,D/A转换电路22将温度值从数字信号转换成模拟电流信号,输出工程控制中常用的4~20毫安标准电流信号。超声波换能器是压电式传感器。Referring to Fig. 1, this thermometer mainly consists of
参见图2,是超声波换能器E1上的驱动信号,它是在FPGA中产生的数字正弦信号经D/A转换电路转换成模拟正弦信号,然后再经功率放大电路放大而成,图中的V代表信号的电压,t代表时间。该信号的频率为1MHz,电压约10V,电流约1.5A,具有约15瓦的电能,足以驱动超声波换能器E1将电能转换为机械能,发出超声波信号。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.
参见图3,是在换能器E2上输出的超声波回波信号,图中的V代表信号的电压,t代表时间。换能器E1发出的超声波信号经过一定的传播时间后传播到换能器E2上时,换能器E2将超声波信号的机械能转换为电能,输出超声波回波信号。换能器E2输出的电信号在超声波没有传播到换能器E2上以前,幅值为零,换能器E2接收到超声波信号后,输出的电信号幅值逐渐增加,然后逐渐减小衰减至零,是一个变幅周期信号,幅值最大的那个波对应于超声波信号的最后一个波。超声波回波信号的频率取决于超声波信号的频率,也是1MHz。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.
参见图4,CPU19向FPGA18中的同步电路432发出开始采样命令后,FPGA18同时启动对超声波换能器E111的驱动和对超声波换能器E212输出信号的采样。Referring to FIG. 4 , after the
构建于FPGA内的数字正弦信号发生器431发送频率为1MHz的8个周期的正弦信号,该信号经过D/A转换电路13转换为模拟信号,再经功率放大电路14放大后,加载在换能器E111上,发出超声波信号。换能器E212输出的电信号经过运算放大电路15放大后,经过滤波电路16滤波后连接到A/D转换电路17。FPGA内部的采样电路433控制A/D转换电路443将模拟信号转换为数字信号,并把采样值逐一存入构建于FPGA内的RAM存储区434中。采样完成后,FPGA430向CPU 19发送采样结束状态信息,CPU19接收到采样结束状态信息后,结束一次采样。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/
采样结束后,CPU19首先根据FPGA内的数字正弦信号发生器431的数据精确确定超声波信号中起点所对应的时刻TQD。After the sampling is finished, the
然后CPU19发出读数据命令,读取暂存于RAM存储区434中的数据,精确计算超声波传播时间终点所对应的时刻。Then the
超声波传输时间终点所对应的时刻是通过对回波信号所有采样数据用细分插补算法进行分析和计算而实现的。参见图5a,分析超声波换能器E2输出的超声波回波信号可知,为保证测量的重复性,应该在峰值幅值最大的波形中提取超声波传输时间的终点。在这个波形的整周期内,最明显的两个特征点是峰值点和过零点,把过零点确定为回波信号的时间参考点更容易获得高精度。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.
参见图5a,本发明的超声波传输时间终点所对应的时刻的计算方法是: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:
首先逐点比较A/D采样点,找出采样点的最大值就可以很容易的确定幅值最大的波形,可以把这一波形称之为特征值波形;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;
其次,参加图5b,确定超声波传输时间终点所对应的过零点P0前面一个采样点P和后面一个采样点P+1,显然在特征波内采样点P的采样值大于零,采样点P+1的采样值小于零;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;
最后,以采样点P和P+1两点对应的时刻作为基准,用细分插补算法可以准确计算出过零点P0所对应的时刻,具体计算方法如下: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:
设A/D的采样频率为FA/D,相邻两个采样点之间的时间即采样周期为TA/D;从第一个采样点到采样点P之间的采样数为N,采样点P对应的采样值为V1,采样点P所对应的时刻为T1;采样点P+1对应的采样值为V2;采样点P所对应的时刻为T1,采样点P与过零点P0之间的时间为T2,过零点P0对应的时刻为TZD,超声波的传输时间为T,则: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:
在过零点附近较小的区域内,正弦波的波形接近于直线,可以根据直线插补的方法确定T2: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:
则过零点所对应的时刻,即超声波传输时间终点所对应的时刻为:Then the moment corresponding to the zero-crossing point, that is, the moment corresponding to the end of the ultrasonic transmission time is:
从上式可知,超声波传输时间终点所对应时刻的分辨率为:It can be seen from the above formula that the resolution of the time corresponding to the end point of ultrasonic transmission time is:
参加图5b,假设超声波回波信号的频率为1M,则周期为1us;A/D的分辨率是12位,那么可以将信号的幅值分为4096份,设A/D的采样频率为32MHz,则在正弦波正的最大值到负的最大值的半个周期内,可以最多采16个点,如果把正弦波正的最大值到负的最大值的半个周期内的波形看作是直线,则显然可知: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:
观察正弦波正的最大值到负的最大值的半个周期内的波形可以看出,过零点附近曲线的斜率远大于峰值附近曲线的斜率,则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>256V2-V1>256
参见图5,超声波的传输时间为:Referring to Figure 5, the transit time of ultrasonic waves is:
由于超声波传输时间起点所对应的时刻可以精确确定,则超声波传输时间测量的分辨率取决于超声波传输时间终点所对应时刻的分辨率,则超声波传输时间测量的分辨率小于0.122纳秒。安装在管体两端的换能器E1和E2之间的距离是固定的,根据测得超声波在换能器E1和E2之间的传播时间,结合在不同温度下和不同介质中超声波的速度,就可以计算得到温度传感器的温度。例如,20℃时超声波的速度是344米/秒,21℃时超声波的速度是344.6米/秒,如果换能器E1和E2之间的距离是0.3米,则在20℃时超声波的传输时间是8.7209×10-4秒,在21℃时超声波的传输时间是8.7057×10-4秒,在21℃时和20℃时超声波的传输时间差为1.52×10-6秒。如上所述,超声波传输时间测量的分辨率优于1.0×10-9秒,则可以实现分辨率优于0.001℃的温度测量。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.
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