毕业设计说明书
基于单片机的超声波流量计
摘 要
测量流体流量的仪表统称为流量计或流量表，流量计是工业测量中重要的仪表之一。超声波流量计与以往传统的流量计相比，具有很多优点，是一种非常理想的节能型流量计。
本设计在查阅大量文献资料的基础上，选择了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。主要进行了以下的详细研究：
1.
研究了时差法超声波流量计的测量原理，对超声波在流体中传播特性及超声波换能器的特性及安装选择进行了深入研究； 2.
在测量精度的提高方面，讨论并采用了超声波时差测量的新方法—多脉冲测量法。 3.
关键词：超声波流量计；单片机；超声波换能器；时差法；多脉冲声循环法
对流量计的硬件电路及软件编程进行了详细的设计分析
The ultrasonic flowmeter based on Monolithic integrated circuit
Abstract
The appliance to measure the rate of fluid flow is generally called flowmeter or flow indicator and is an important appliance in industrial measurements. Compared with traditional flowmeter, the ultrasonic flowmeter has many advantages.
This design based on mass research of data and finally took the travel-time-difference method ultrasonic flowmeter as the object of study and made deep theoretical research of how to improve the accuracy, stability and reliability of the system.
1. Studies on the measurement principles of travel-time-difference method ultrasonic flowmeter were made. The dissemination features of ultrasonic wave in fluid and the features of Ultrasonic wave transducer and the choice of different methods of installation.
2. From the aspect of the enhancement of measure accuracy, it discussed the new method of travel-time-difference---multi-beams measurements and further put it into application.
3. Detailed design and analysis of the hardware circuit and software programming of the flowmeter were made.
Key words: ultrasonic flowmeter；Monolithic integrated circuit；ultrasonic transducer； travel-time-difference method；multi-beams Sound cyclic method
目 录
摘 要 ......................................................................................................................................... I Abstract .................................................................................................................................... II 第一章 概述 .............................................................................................................................. 1
1.1 超声的相关概念 ......................................................................................................... 1
1.1.1 超声的相关概念 .............................................................................................. 1 1.1.2 超声的研究发展和应用 .................................................................................. 1 1.2 流量计的发展历史及现状 ......................................................................................... 2 1.3 流量计的分类及特点 ................................................................................................. 3 1.4 超声波流量计概述 ..................................................................................................... 3
1.4.1 超声波流量计的发展及现状 .......................................................................... 3 1.4.2 超声波流量计的特点 ...................................................................................... 3 1.4.3 超声波流量计两种主要测量原理及对比 ...................................................... 4
第二章 超声波流量计的总体设计 .......................................................................................... 5
2.1 超声波换能器概述 ..................................................................................................... 5
2.1.1 超声波换能器能量转换原理 .......................................................................... 5 2.1.2 超声波换能器的类型及主要性能指标 .......................................................... 5 2.2 超声波换能器的选择及设计 .................................................................................... 7
2.2.1 超声波换能器的主要参数 .............................................................................. 7 2.2.2 超声波换能器的选择 ...................................................................................... 8 2.2.3 超声波换能器的安装方式及选择 .................................................................. 8 2.3 时差法测量原理及影响测量的主要因素 ................................................................. 9
2.3.1 Z型安装方式时差法测流量的测量原理 ....................................................... 9 2.3.2 影响测量的主要因素 .................................................................................... 11 2.3.3 V型安装方式时差法原理介绍 ..................................................................... 11 2.4 多脉冲测量原理 ....................................................................................................... 12 第三章 超声波流量计一次仪表部分硬件设计 .................................................................... 15
3.1 超声波发射电路的选择与设计 .............................................................................. 15 3.2 超声波接收信号调理电路选择与设计 .................................................................. 16
3.2.1 一级放大电路 ................................................................................................ 16 3.2.2 带通滤波电路 ................................................................................................ 17 3.2.3 二级放大电路 ................................................................................................ 18
第四章 超声波流量计二次仪表部分硬件设计 .................................................................... 19
4.1 系统工作原理概述 ................................................................................................... 19 4.2 芯片资料 ................................................................................................................... 21
4.2.1 总线收发器74LS245 .................................................................................... 21 4.2.2 计数器74S196 ............................................................................................... 21 4.2.3 4040CMOS12级二进制计数分频器 ............................................................ 22 4.2.4 AT89C51 ......................................................................................................... 23 4.3 超声波顺流逆流发射接收控制电路 ....................................................................... 25 4.4 计数电路原理概述 ................................................................................................... 26 4.5 从单片机的作用及选择 ........................................................................................... 27 4.6 主单片机的作用及选择 ........................................................................................... 28 4.7 显示电路 ................................................................................................................... 28
4.7.1 LED显示器的结构和原理 ............................................................................ 28