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摘要在PLC问世以前，工业电气控制领域一直是以继电器系统控制占主导地位。由于继电器系统存在控制系统体积大、可靠性低、查找和排查故障困难等特点，PLC出现后迅速发展起来成为当代工业自动化的支柱产业之一。58587
S7-200PLC可应用的范围非常广泛，但是CPU所能扩展的模块最多为7个，在大工程的应用中考虑到成本，选用S7-200PLC完成工作时需要使用多个PLC来实现。随着PLC的数量增加，通信链路也相应的增加，仅仅使用单一链路来完成通信的话，出现故障的可能性增大，可靠性降低。
本论文为了解决这个问题，用两台S7-200PLC模拟多台S7-200PLC系统情况，在PLC与上位机相连的基础上，用以太网和PPI两种通信方式使两台PLC之间互相备份上位机所需的数据。当相互备份的两台S7-200PLC的一条通信线路出现问题的时候，另一条通讯链路保证数据备份的同时，有检测报警系统，提醒工作人员及时检修，防止两种通信链路先后出现故障，提高系统的可靠性。证明这个方案可以实现。
毕业论文关键词：S7-200PLC；数据传输；通信协议；
Abstract Before the arrival of PLC, industrial electrical control field has always been dominated by relay control. Due to relay control's large size of the control system, the low reliability, and the difficulty in finding and troubleshooting, PLC has developed rapidly after appearing and become one of the pillar industries of modern industrial automation.
As we all know, the S7-200 PLC can be widely used, but CPU can extend the module no more than seven. When taking the cost into consideration to use S7-200 PLC in the application of large engineering, it is required to use multiple PLC to implement the work. With the increasing number of PLC, the communication link increases correspondingly. Using a single link to complete the communication, the possibility of failure increases and the reliability reduces.
To solve this problem, this project uses two S7-200 PLC to simulate the system condition of multiple S7-200 PLC. Based on the connection of PLC and PC, it use the two communication ways of Ethernet and PPI to make two PLC backup the data required by PC to each other .When one communication link of the two mutual backup S7-200 PLC has problem, another communication link need proper detection alarm system to remind staff repairing promptly while ensuring data backup. It can prevent two kinds of communication has failure one after another and improve the reliability of the system. At last, this project proves that the program can be implemented.
Keywords: S7-200 Programmable Logic Controller; data transmission; Communication Protocol;
第一章 绪论 1
1.1 研究背景和意义 1
1.1.1 数据备份和链路冗余 1
1.1.2 研究意义 1
1.3 主要完成内容 2
第二章 S7-200PLC介绍 4
2.1 S7-200PLC的CPU模块 4
2.1.1 CPU模块外形结构 4
2.1.2 CPU模块主要性能 4
2.2 S7-200PLC的通信扩展模块 5
2.2.1 EM277模块 6
2.2.2 调制解调器模块EM241 6
2.2.3 工业以太网通信模块 7
2.3 STEP7-MICRO/WIN编程软件 7
2.3.1 STEP7-Micro/WIN编程软件介绍