IC693ACC333
IC693ACC333
IC693ACC333
PLC除逻辑运算外,控制回路用的算法功能已经大大加强,但PLC用梯形图编程,模拟量的运算在编程时不太直观,编程比较麻烦。但在解算逻辑方面,表现出快速的优点,在微秒量级,解算1k逻辑程序不到1毫秒。它把所有的输入都当成开关量来处理,16位(也有32位的)为一个模拟量。
而DCS把所有输入都当成模拟量,1位就是开关量。解算一个逻辑是在几百微秒至几毫秒量级。对于PLC解算一个pid运算在几十毫秒,这与DCS的运算时间不相上下。
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。
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