After the 1980s,in addition to logic operations,the algorithm functions used in PLC control loops have been greatly enhanced,but PLCs are programmed with ladder diagrams,and the operations of analog quantities are not intuitive in programming,and programming is more troublesome.However,in terms of solving logic,it shows the advantage of being fast,in the order of microseconds,it takes less than 1 millisecond to solve a 1k logic program.It treats all inputs as switch quantities,16-bit(and 32-bit)as an analog quantity.
The DCS regards all inputs as analog quantities,and 1 bit is the switch quantity.Solving a logic is on the order of hundreds of microseconds to several milliseconds.For plc to solve a pid operation in tens of milliseconds,which is comparable to the operation time of dcs.
80年代以后，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。
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