Early PLCs were dominated by sequential control of digital quantities.With the continuous expansion of PLC functions,PLC has added analog control functions,PID adjustment functions,communication networking functions,and hierarchical control functions.But it is difficult for PLC to form a large-scale,complex and comprehensive system.If too many PCs attempt to communicate with too many PLCs through the network,it may lead to bottlenecks and timing difficulties.
早期的PLC以数字量的顺序控制为主。随着PLC功能不断扩充，PLC增加了模拟量控制功能、PID调节功能、通讯联网功能及分级控制功能等，在过去DCS占统治地位的化工、冶金等行业也可由PLC进行控制。但PLC难以组成大型、复杂、综合的系统，如果过多的PC企图通过网络与过多的PLC通讯，则可能导致瓶颈现象及计时上的困难。
HP/Agilent 83410C Optical Lightwave Receiver
HP/Agilent 83400B Lightwave Source, 1300 nm, 3GHz
HP/Agilent 8563E Front Panel Assembly
EXFO FOT-910 Fiberoptic Test System
HP/Agilent 08591-60098/60107 Board Assembly Countlock
Yokogawa TA320 Time Interval Analyzer
HP/Agilent 5086-7413 Sampler, Fully Tested
