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摘要

本次毕业设计的课题是基于PLC的液位控制系统的设计。在设计中，笔者主要负责的是数学模型的建立和控制算法的设计，因此在论文中设计用到的PID算法提到得较多，PLC方面的知识较少。

本文的主要内容包括：PLC的产生和定义、过程控制的发展、水箱的特性确定与实验曲线分析， FX2系列可编程控制器的硬件掌握，PID参数的整定及各个参数的控制性能的比较，应PID控制算法所得到的实验曲线分析，整个系统各个部分的介绍和讲解PLC的过控制指令PID指令来控制水箱水位。

关键词：FX2系列PLC，控制对象特性，PID控制算法，扩充临界比例法，PID指令，实验。

The liquid level control system based on PLC

ABSTRACT

The subject of graduation design is based on PLC, liquid level control system design. In the design, the author is mainly responsible for the mathematical model and control algorithm design, so the design used in the paper referred to was more PID algorithm, PLC in less knowledge.

Main contents of this article: PLC creation and definition, process control, development, and water tanks and experiment to determine the characteristics curve analysis, FX2 series PLC , the application PID control algorithm obtained experimental curve analysis, the entire system, introduce and explain the various parts of the PLC process control commands to control the tank level PID instruction.

Keywords：FX2 series PLC, the control object characteristics, PID control algorithm, to expand the critical proportion method, PID instruction, experimental.

目 录

中文摘要 .......................................................................................................................................... I 英文摘要 ........................................................................................................................................ II 1 绪论 .............................................................................................................................................. 1

1.1 PLC的产生、定义及现状 ................................................................................................... 1

1.1.1PLC的产生、定义 ...................................................................................................... 1 1.1.2PLC的发展现状 .......................................................................................................... 1 1.2过程控制的发展 .................................................................................................................... 2 1.3本文研究的目的、主要内容 ................................................................................................ 3

1.3.1本文研究的目的、意义 ............................................................................................. 3 1.3.2本文研究的主要内容 ................................................................................................. 3

2 FX2系列PLC和控制对象介绍 .................................................................................. 5

2.1 三菱PLC控制系统 ............................................................................................................. 5

2.1.1 CPU模块 .................................................................................................................... 5 2.1.2 IO模块 ........................................................................................................................ 6 2.1.3电源模块 ..................................................................................................................... 6 2.2 过程建模 ............................................................................................................................... 6

2.2.1 一阶单容上水箱对象特性 ........................................................................................ 6 2.2.2 二阶双容下水箱对象特性 ...................................................................................... 11

3 PID调节及串级控制系统 .......................................................................................... 15

3.1 PID调节的各个环节及其调节过程 .................................................................................. 15

3.1.1比例控制及其调节过程 ........................................................................................... 16 3.1.2比例积分调节 ........................................................................................................... 16 3.1.3比例积分微分调节 ................................................................................................... 17 3.2 串级控制 ............................................................................................................................. 18

3.2.1串级控制系统的结构 ............................................................................................... 18 3.2.2串级控制系统的特点 ............................................................................................... 19 3.2.3串级控制系统的设计 ............................................................................................... 19 3.3 扩充临界比例度法 ............................................................................................................. 21 3.4 三菱FX2系列PLC中PID指令的使用 ......................................................................... 22 3.5在PLC中的PID控制的编程 ........................................................................................... 23

3.5.1回路的输入输出变量的转换和标准化 ................................................................... 23 3.6变量的范围 .......................................................................................................................... 25