时差法超声波流量计_2006_硕士论文-

重庆大学硕士学位论文中文摘要

摘要

超声波流量计由于具有非接触式测量、测量范围宽、安装简便、以及特别适合大管径及危险性流体流量测量等优点，被供水、石油、化工、电力等部门广泛应用。然而，由于超声波流量计只是在近几十年才出现的一种新型仪表，还有很多不完善的地方，比如成本较高、精度不够等，有必要对其加以改进和提高。

本论文通过充分调研及查阅大量的文献资料，选择时差法超声波流量计为研究对象，对如何提高系统的精度及系统稳定性和可靠性问题进行了深入的理论研究，并设计了具体的硬件电路，主要工作及创新有：

1.研究了几种超声波流量计特别是时差法超声波流量计的测量原理，对超声波在流体中的传播特性及超声波换能器进行了较深入的研究；根据流体力学及物理学的有关知识，对超声波流量计进行了修正，并给出了不同情况下流量修正系数的计算公式；

2.针对传统时差法超声波流量计测量精度易受温度影响的问题，采用了改进型算法，在很大程度上避免了温度变化对测量精度的影响；介绍了几种常用提高超声波测时精度方法的同时，讨论并采用了超声波时差测量的新方法——多脉冲测量法的原理和应用；

3.结合课题的实际情况，对时差法超声波流量计的硬件电路进行了详细的分析和设计，讨论了器件的选择、参数计算等技术问题，设计出了匹配性能良好的发射、接收电路；在信号调理上，除了常规的滤波电路外，还采用了自动增益放大电路来提高信号的可靠性；而且，采用主从单片机协同工作的方式，提高了系统的稳定性；在软件方面，给出了系统的软件流程图并较详细地叙述了算法的实现；

4.针对流量计的工作环境，对流量计系统的抗干扰性进行了研究，并采取了相应的软、硬件措施；

5.对造成超声波流量测量误差的各种因素进行了详细的分析、研究，并应用误差理论，对时差法超声波流量计的各种可能的误差进行了误差分配和合成；对硬件电路和软件进行了试验性的验证，给出了实验结果。

关键词：超声波流量计，时差法，传播时间

ABSTRACT

Ultrasonic flowmeter has been widely used in waterworks,oil industry,chemical industry and electric power plant in virtue of its many advantages,such as non-contact, wide measurement scope,convenience of installation,especially acceptable for measurement of large flow and flow in dangerous environment.However,the ultrasonic flowmeter develops just some ten years,and has some disadvantages,thus it is necessary to make modification and advance.

After deep market investigation and many references about the ultrasonic flowmeter,we choose time-difference-type ultrasonic flowmeter for our study objects. The article makes deep theoretical research on the problem of improving accuracy, stability and reliability.In addition,it supplies the designs of circuits.Generally,there are five parts as the following:

1.Expouded the principles of some ultrasonic flowmeter,especially about the time-difference-type ultrasonic flowmeter;researched the transducer the propagation character of ultrasonic in fluid.Then the ultrasonic flowmeter was corrected according to the theory of hydromechanics and physics,and calculation formulae of the flow revision coefficient are given under different state.

2.On account of the problem that the accuracy of traditional ultrasonic flowmeter is easily influenced by temperature,adopt an improved algorithm which can avoid the influence on accuracy by temperature variation to some extent;introduce several means about precise measurement on propagating time,meanwhile,discuss the theory and application of a brand new measurement method--the multi-beams method deeply.

3.Taking the study into consideration,analyze and design the hardware circuit of flowmeter in detail,discuss some technical matters such as chip selection and parameters calculation,design a better matching emitting and receiving circuits,use routine filter circuit and automatic gain control circuit to adjust signal;furthermore, with the help of double MCU,the resist ability of system to disturbing is improved strongly.In software,the soft flow chart of system and the design idea of the system are given.

4.Considering the environment the ultrasonic flowmeter worked,the anti-jamming of the flowmeter system are discussed,and the corresponding methods of soft and hardware are adopted to minish or remove the interfere.