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.
对湖北省城市体系的规模等级、城市职能、地域空间结构的特征进行了分析研究。
This paper analyzes the characteristics of the urban scale and scale grade, the urban function, and the region space structure of Hubei urban system.
结果表明：（1）武汉市星级饭店在等级规模上表现为纺锤形结构，在空间分布上呈现出核心-边缘结构；
It is found out that:(1)the rating-scale of the Star Hotels in Wuhan City is a spindle structure, and their spatial distribution reveals to be a core-peripheral structure;
结果表明：（1）武汉市星级饭店在等级规模上表现为纺锤形结构，在空间分布上呈现出核心-边缘结构；
It is found out that:(1)the rating-scale of the Star Hotels in Wuhan City is a spindle structure, and their spatial distribution reveals to be a core-peripheral structure;
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