现代化工业生产线通常由多个不同的加工单元构成，每个加工单元一般由一台PLC控制。由于各加工单元之间需要按照生产工艺协调动作，所以各加工单元的PLC并非独立使用，而是利用网络实现集中控制。在网络中起指挥管理作用的PLC称为主站，处于服从地位的称为从站，从而形成“主站集中管理，从站分散控制”。该设计建立了由2台西门子S7-200 PLC构成的主从站网络控制系统，实现了对从站上连接的异步电机变频控制和运行状态实时信息显示等功能。%Modern industrial production line is usually consists of a number of different processing u-nits, each processing unit is generally controlled by a PLC. Due to the need according to the production process between each processing unit coordinated action, so each PLC of processing unit is not used inde-pendently, but use a network to realize centralized control. In command management role of PLC network known as the master station, obedience is the status of the called from station, thus forming“master sta-tion centralized management and from station decentralized control”. This design was established by 2 sets of Siemens S7 -200 PLC of master -slave station network control system, realized the frequency conversion control of asynchronous motor from a standing and real-time information display, and other functions.
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