USB-6525 NI
可编程控制器按扫描方式工作,分散控制系统按用户程序的指令工作。因此,可编程控制器对每个采样点的采样速度是相同的,而分散控制系统中,可根据被对象的特采用不同的采样速度,例如,流量点的采样速度是1S,温度点的采样速度是20S等。此外,在分散控制系统中,可以设置多级中断优先级,而可编程控制器通常不设置中断方式。
存储器容量上,可编程控制器所需运算大多是逻辑运算,因此,所需存储器容量较小,而分散控制系统需进行大量数字运算,存储器容量大。运算速度方面,模拟量运算速度可以较慢,而开关量运算需要较快的速度。抗干扰和运算精度方面,两者也有所不同,例如,开关量的抗干扰较模拟量的的抗干扰要强,模拟量的运算精度要求较高等。
分散控制系统的分散过程控制装置安装在现场,除需按现场的工作环境设计外,分散控制系统的装置通常根据安装在控制室的要求设计。可编程控制器是按照工作环境的要求设计,因此在元器件的可靠方面需有专门的考虑,对环境的适应也需专门考虑,以适应恶劣工作环境的需要。
随着应用范围的扩展,可编程控制器和分散控制系统、现场总线控制系统、数据采集和系统相互渗透,互相补充。例如,可编程控制器扩展模拟量控制的功能,分散控制系统扩展开关量控制的功能等,出现“你中有我,我中有你”的综合集成趋势。
基于PLC的特点,PLC已得到广泛的应用。目前主要是:
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