摘 要：现代液位控制系统的规模日趋大型化、复杂化，液位控制已成为目前过程控制领域的一个研究热点。本文设计了一种基于单片机与PLC的液位控制系统，该系统以单片机与PLC控制处理为核心，由超声波测量液位模块，显示模块，报警模块，单片机与PLC通讯模块和PLC控制模块。给出了相应的软件设计流程图、电路接口原理图和C语言程序，并用Proteus仿真验证。系统采用8051单片机作为液位测量显示系统的数据处理核心；采用超声波实现对液位的测量；采用数码管实现对液位数据的显示。单片机与PLC通过RS-485通讯，PLC根据液位信息控制水泵运行。系统能够自动测量液位，并根据液位控制水泵运行；当液位越限时自动报警。56954

毕业论文关键词：液位测量，单片机，PLC，超声波传感器，数码管

Abstract: The scale of Modern liquid level control system tends to be more upsizing and complex. Nowadays, it has become a research hotspot in process control field. Based on single chip microcomputer and PLC, this article has designed a kind of liquid level control system. Single chip microcomputer and PLC is used as a central processing and control component in the system which consists of ultrasonic liquid level detect module, display module, alarm module, single chip microcomputer and PLC communication module and PLC control module. This article gives corresponding software design flow chart, interface circuit schematic diagram and the C application program, and uses the Proteus software to test simulation. 8051 single chip microcomputer is used as data-processing core in liquid level measurement display system. The system also adopts ultrasonic liquid level measurement and digital number display indicator. Single chip microcomputer and PLC communication, PLC according to the level of information control pump operation. The system can realize automatic water level measurement and control pump running according to water level; if water level exceed the limit, the system will sound an alarm.

Keywords: Level measurement, microcontroller, PLC, ultrasonic sensors, digital tube

目  录

1  绪论 4

1.1  课题背景与研究意义 5

1.2  国内外研究现状及发展 5

1.3  本课题主要研究内容 6

2  总体设计方案 6

3  单片机模块 7

3.1  电路原理图 7

3.2  8051单片机 8

3.3  超声波测液位原理 10

3.4  超声波信号的发射与接收电路 11

3.5  软件设计 15

3.6  键盘输入 16

3.7  报警接口电路 17

3.8  液位状态显示接口电路 18

4  单片机与PLC通讯 19

4.1  硬件以及通讯原理分析 19

4.2  通信系统设计 20

5  PLC控制水泵 21

5.1  选型 21

5.2  PLC的工作方式 21

5.3  PLC的基本工作原理 22

5.4  PLC控制水泵主电路 23

5.5  PLC与软启动器接线