双频超声波多普勒流量计的研究与设计

【作者】 亓月刚；

【导师】 李明伟；

【作者基本信息】 大连理工大学 ， 通信与信息系统， 2004， 硕士

【摘要】 超声波多普勒流量计主要用于污水类非纯净液体和固体颗粒的两相流的流量测量，它具有分辨率高，对流速变换响应快，对流体的压力、粘度和温度等因素不敏感的优点，但超声多普勒流量计的精度和稳定性对于高精度测量要求，还是满足不了要求，我们采用双频多普勒技术(DFD)很好地解决了这个问题，因此双频超声波多普勒流量测量技术的研究是一项非常有实用价值的研究课题。 在原我们成功研制的单通道超声波多普勒流量计的基础上，通过查阅文献和理论分析，本文建立了双频多普勒测量方法的理论基础，实验验证了这一理论的可行性。在此基础上，设计了一套完整以TI公司的TMS320F240 DSP作为核心处理器件的双频多普勒流量计测量系统，该系统不仅具有瞬时流速、流量、累计流量等显示功能，还具有电流输出(4～20mA)和多普勒频谱动态显示的功能，有利于实时观测信号状态，特别是对流量计的安装非常有利。 与传统的单频多普勒流量测量不同，双频超声波多普勒流量测量系统产生两组异频、独立的超声波信号，两种频率用于识别信号，它能有效去除噪声信号，并将准确识别出的多普勒信号进行平方放大。 本系统引入先进的数字信号处理技术，在频域上对多普勒信号进行有效的处理。具体方法是首先对两个通道的多普勒信号采样，分别进行FFT变换求其功率谱；然后将其中一个通道的功率谱移位，使流量多普勒信号频移重叠而噪声被错开；将两束信号的功率谱相乘，结果多普勒信号被平方放大，而噪声信号被大大衰减，使多普勒信号更加容易识别和跟踪；再在相乘后的功率谱上应用峰值逼近法，加上适当的数字滤波技术得到较精确的多普勒频移值；最后根据多普勒效应原理，求取管道中流体的流速及其它数据量。其软件稳定性好，效率高，操作灵活方便。 最后对实验数据进行了分析，结果表明，采用双频多普勒技术大大提高了仪表的精度和稳定性。更多还原

【Abstract】 Ultrasonic Doppler flowmeter is mainly applied to measure flux of sewage or other liquid with solid grain. It is of high resolving power, and can respond quickly with the variety of velocity, moreover, it is insensitive to the pressure and temperature of liquid. But its accuracy and stabilization must be improved in further. Dual-frequency Doppler technology can solve it. Therefore research of dual-frequency ultrasonic Doppler flowmetere is significative.On the basis of measurement principle of single-channel Ultrasonic Doppler flowmeter , referring to an amount of literatures, this paper puts forward theory of measurement of Dual-frequency Doppler flowmeter, and experiments qualitatively proved that this method is practicable. Dual-frequency Doppler measurement system is designed with a TMS320F240 DSP as the core. The system designed displays not only the velocity and flux but also the dynamic spectrum of Doppler, which is advantageous during its installation, besides a standard current (4~20mA) is available.Unlike to the conventional Doppler flowmeter, Dual-frequency Ultrasonic Doppler flowmeter generates two independent frequencies. The two frequencies are used to automatically identify signal and eliminate noise, the Doppler information is squared .This makes the Doppler information easier to identify and track.In the system, digital signal processing is introduced to analyze Doppler signal. First the data collected from each transmission contains both Doppler and noise information. FFT is required to get the power spectrum of the data. Second one set of collected data is then shifted by a ratio of the transmission frequencies. This process aligns the Doppler information in the same frequency domain, while noise is misaligned. Third once the Doppler information is aligned, the two sets of data are multiplied. As a result, the Doppler information is squared and noise falls away. This makes the Doppler information easier to identify and track. At last The algorithm of approaching peak value applies in the power spectrum. Thus Doppler frequency shift is obtained. According to Doppler effect, velocity and flux can be calculated.Experimental results show that Dual-frequency Doppler technology makes flwometer more accurate and stable.更多还原