6ES7138-4CA60-0AB0 想要它来亿佳
逻辑关系图反映了控制过程中控制作用与被控对象的活动，也反应了输入与输出的关系。 3. 绘制电路图 绘制电路的目的，是把系统的输入输出所设计的地址和名称联系起来。这是很关键的一步。在绘制 PLC 的输入电路时，不仅要考虑到信号的连接点是否与命名一致，还要考虑到输入端的电压和电流是否合适，也要考虑到在特殊条件下运行的可靠性与稳定条件等问题。 在接地电阻方面，对plc也许要求不高，但对dcs要在几欧姆以下（通常在4欧姆以下）。模拟量隔离也是非常重要的。 相同i/o点数的系统，用plc比用dcs，其成本要低一些（大约能省40%左右）。plc没有操作站，它用的软件和硬件都是通用的，所以维护成本比dcs要低很多。如果被控对象主要是设备连锁、回路相对很少，采用plc较为合适。如果主要是模拟量控制、并且函数运算很多， 采用dcs。dcs在控制器、i/o板、通讯网络等的冗余方面，一些 运算、行业的特殊要求方面都要比plc好的多。plc由于采用通用监控软件，在设计企业的管理信息系统方面，要容易一些。
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