【作者】 赵宇洋；

【导师】 张涛；

【作者基本信息】 天津大学 ， 检测技术与自动化装置， 2008， 硕士

【摘要】 超声波流量计作为一种非接触、易于安装维护的仪表在工业领域得到广泛应用。尤其在天然气计量领域,超声波流量计的潜力和优势十分明显。虽然孔板流量计仍是主要测量手段,但超声波流量计具有无可动部件、无压损、测量精确度高等优点,另外随着相关标准的发布和实用领域的探索,超声波流量计将会得到越来越广泛的应用。本文将伪随机编码信号引入了相关时差法超声流量计的信号处理中。相关时差法是传统时差法与相关算法对结合,兼具二的者优点,并且克服了时差法触发时刻不易确定、时间差难以直接精确测量,相关法被测对象不确定、易受驻波影响等缺点。伪随机编码码信号以其优良的自相关特性,可以实现对微小时间差的精确测量。本文针对巴克序列,m序列以及L序列进行了理论分析及相关试验,比较了各编码方式的特性,并对影响相关结果的重要参数,如:码元宽度,采样频率,序列长度,序列周期个数等,确定了选取标准。系统硬件电路主要包括超声信号的发射、接收和处理部分。发射部分设计了数字式任意波形发生器,直接产生经过调制的伪随机编码信号。超声信号接收处理电路的作用是从放大滤波后的信号中解调出伪随机编码信号,并将其稳定在一个固定的范围之内。使用任意波形发生器对本课题选用的SensComp发射/接收型压电陶瓷超声换能器进行了调幅编码特性实验研究,得出参数选择的标准。系统调试成功后,分别用巴克序列、m序列、L序列三种不同编码方式激励超声换能器,比较优劣;并将本设计伪码相关时差法超声波气体流量计在天津大学过程检测与控制实验室的常压气体流量实验装置上进行了试验测试,对测试结果的误差来源进行了详细的分析,并提出了解决和进一步完善设计的方案。更多还原

【Abstract】 Ultrasonic flowmeter is applied widely in industrial measureing filed, because of its advantages of noncontact installation and maintenance with ease. In the filed of natural gas measuring, ultrasonic flowmeter has evident potential and advantages, such as without mobile component, without pressure loss and high precision in measurement. With relevant standards promulgated and practicality explored, ultrasonic flowmeter must be developed at this filed in the future.Pseudo Random code is introduced to the correlation time-difference method of ultrasonic flowmeter. Correlation time-difference method combines traditional time-difference method with the correlation method, and inherits their merits. To ensure the sharp figure, the pseudo random code, due to their variety and simplicity, served as the modulation signals in the proposed method. The simulations were carried out to configure the coded waveform parameters including sequence length, code width and code amplitude.The experimental part of this investigation details how to encode the ultrasonic waveform. Hardware system is composed of the emission, reception and procession of the ultrasonic signal. The emission part is designed of random waveform generator, which can generate Pseudo Random code directly. The reception and procession part is responsible to demodulate Pseudo Random signal from the ultrasonic signal after amplified and filtered, and restricted in the anticipant range.Using the digital random wave generator, carry through the coding characteristic experiment on the SensComp ultrasonic transceiver piezoelectric transducer. By means of sampling the coded ultrasonic signals and correlating them through mathematic software, compared the results of different coded manners, such as Barker-sequences, m-sequences, and L-sequence. The system finally got verified on the gas flow facility at the Process Detect and Control laboratory in Tianjin University.更多还原