城市规模等级结构的划分是一个多指标的分类问题。
The division of city hierarchical structure is a multi-index classification problem.
城市体系结构是等级规模、职能和网络的综合反映。
The structure of urban system is the reflection of urban size, function and network.
本文主要介绍了在实际工业系统中常见的PLC网络结构及其通讯方式。针对工业系统中plc网络的规模、等级，给出使用的方法。
In this paper, the structures and communication means of PLC Net in the automation industry system are summarized and their usage methods are narrated according to their size and grading.
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