基于LabVIEW的液位测控系统设计

本科毕业设计论文

摘 要

液位计算机测量与控制实验系统是为西北工业大学航空学院民航工程系综合实验平台而开发的课程教学实验系统。液位测量与控制系统集传感器信号的采集、调理、转换、检测和控制为一体，是实时交互式图形界面应用系统。该系统采集液位信号并用计算机可视化界面实时显示液位高度的变化过程；通过交互式对话框设置期望的液位高度，在检测当前液位的基础上控制进/出水阀门，从而对实际液位高度进行控制。

论文介绍了液位计算机测量与控制系统的结构与功能；分析了硬件系统中测量与控制电路的组成及工作原理；计算了信号调理电路中测量放大器的增益及各元件参数；使用PROTEL软件绘制了信号调理电路图；介绍了多功能数据采集卡NI USB-6008的特点、功能及软件开发平台LabVIEW；分析了系统的软件程序；介绍了液位计算机测控系统的用户使用界面所能实现的功能。针对实验系统对液位进行开关控制所带来的问题，提出了用PID控制方法进行改进的措施。

关键词：液位测控，压力传感器，信号调理，NI USB-6008 ，LabVIEW

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本科毕业设计论文

ABSTRACT

The liquid level measurement and control computer experimental system is a course teaching experimental system which is used to develop the comprehensive experimental platform for Aviation Institute of Civil Engineering of NWPU. The liquid level measurement and control system with real-time interactive graphical interface is of the sensor signal acquisition, conditioning, conversion, testing and control functions. The system acquires the signals of liquid level and computer interface real-time to show the liquid level changing process. Through an interactive dialog box, the desired water level is set. The actual water level is controlled based on the current liquid level detection through the import / outlet valves.

The structure and function of the liquid level measurement and control computer experimental system is introduced at first. The hardware system composition and working principle is analyzed, and the gain and each components parameters of measuring amplifier in signal conditioning circuit are calculated. The signal conditioning circuit is drawn with PROTEL, and the features and functions of the multi-function data acquisition card NI USB-6008 and software development platform LabVIEW are introduced. The system software program is also analyzed. For the control problems of import / outlet valves of the liquid level measurement and control computer experimental system, a PID control method is proposed to improve the system performances.

KEY WORDS：liquid level measurement and control，pressure sensor，signal conditioning ， NI USB-6008 ，LabVIEW

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本科毕业设计论文

目 录

摘 要 ................................................................................................................................. I ABSTRACT ..................................................................................................................... II 第一章 绪 论 ..................................................................................................................1 1.1 课题背景 ............................................................................. 错误！未定义书签。 1.2 系统组成 ............................................................................. 错误！未定义书签。 1.3 系统工作原理 ........................................................................................................2 1.4 本文的主要内容 ....................................................................................................2 第二章 传感器及信号调理 ..............................................................................................3 2.1 数据采集 ................................................................................................................3 2.1.1 数据采集技术 .................................................................................................3 2.1.2 数据的采样 .....................................................................................................3 2.2 传感器 ....................................................................................................................4 2.2.1 传感器的选用 .................................................................................................4 2.2.2 压阻式压力传感器的基本原理 .....................................................................5 2.2.3传感器存在的问题及其解决方法 ..................................................................5 2.3 信号调理电路 ........................................................................................................7 2.3.1第一级数据放大器 ..........................................................................................7 2.3.2第二级放大器 ..................................................................................................8 2.4 整体电路 ................................................................................................................8 第三章 液位控制回路 ....................................................................................................11

3.1基本组件及原理特性 ...........................................................................................11 3.1.1六反向器（74LS04） ...................................................................................11 3.1.2 电磁阀 ...........................................................................................................12 3.2继电器 ...................................................................................................................13 3.2.1固态继电器SSR ...........................................................................................14

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本科毕业设计论文

3.2.2交流型SSR的工作原理 ..............................................................................14 3.2.3SSR的注意事项 ............................................................................................16 第四章 计算机液位测控系统 ........................................................................................19

4.1 多功能数据采集卡 ..............................................................................................19 4.1.1数据采集卡的主要性能指标 ........................................................................19 4.1.2数据采集卡(DAQ)的组成 ............................................................................20 4.1.3NI USB-6008数据采集卡 .............................................................................20 4.2 图形化虚拟仪器开发平台—LabVIEW .............................................................22 4.3程序模块化设计概述 ...........................................................................................23 4.4液位测控程序设计 ...............................................................................................24 4.4.1 系统软件需求 ...............................................................................................24 4.4.2 LabVIEW前面版设计 ...............................................................................25 4.4.2 LabVIEW后面板程序设计 .......................................................................26 4.5软件调试步骤及其调试 .......................................................................................27 第五章 系统线性改进 ....................................................................................................29

5.1 PID控制原理 .......................................................................................................29 5.2数字PID控制算法 ..............................................................................................31 5.3 PID控制的局限性及新方法的探求 ...................................................................33 第六章 全文总结 ............................................................................................................35 参 考 文 献 ....................................................................................错误！未定义书签。 致 谢 ..........................................................................................错误！未定义书签。 毕业设计小结 ..................................................................................................................41 附录...................................................................................................................................43 1. 74LS74推荐工作条件 .............................................................................................43 2. 电路板设计步骤 ......................................................................................................44 3. NI USB-6008/6009的I/O 连接器 ..........................................................................44

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