编程设备服务处理的高速化。当扫描时间为数十毫秒时,几毫秒的编程工具和监控设备的服务处理时间不会带来什么问题。但是在执行1毫秒以下的控制任务时,就有必要大大缩短这个时间。所采用的方法是以多芯片并行处理的方式,由专门处理编程及监控服务的微处理器芯片执行这类处理,以减轻对执行控制程序的芯片的影响,让它只管执行顺控和逻辑运算。此外,为了提高服务处理的效率,缩短在现场读写程序的时间,以缩短操作时间,采用了高速的串行通信(大的波特率为115.2Kbps)以及将UCB口(大波特率达12Mbps)引入PLC的模块,从而实现与编程工具及监控设备之间通信的高速化,并允许同时使用这两个通信端口,由多人同时进行编程和调试。
提高外部设备的响应速度。在PLC内部实现高速化的同时,还要提高外部设备的响应速度,才能整体提高整个系统的性能,为此,在缩短I/O模块的输入输出响应时间,提高模拟量输入输出模块的模-数和数-模转换时间,下了不少工夫,以求得系统整体的控制速度达到毫秒级以下。例如,在晶体管输出模块的输出电路中选用高性能的晶体管,使响应时间加快50%;在直流输入模块中,其输入的时间常数回路采用专用ASIC芯片,可通过编程软件选择输入模块的响应时间为1/5/10/20/70毫秒;为提高模拟量模块的转换时间,采用A/D或D/A的专用芯片,是转换速度为原先的1/2—1/6。另外也通过开发专用的处理器和通信专用ASIC,缩短通信网络模块之间的通信链接的循环时间。
信息技术渗入PLC。信息技术渗入PLC是为了适应工厂控制系统和企业信息管理系统日益有机结合的发展趋势;适应在控制层面让不同品牌的PLC之间,让PLC与DCS、SCADA等系统之间,能有效而足够快地交换数据的市场要求。它主要表现在:
1)让以Windows操作系统的PC机嵌入PLC系统[见上述第(1)节]。
2)创建开放的网络环境。如推出能挂100M的高速以太网的Web服务器模块(三菱电机小Q系列的QJ71WS96,横河电机FA-M3系列的F3WBM1-0T-S01),模块内的软件捆绑了目前常用的TCP/IP、UDP/IP等传输层和网络层的规约,以及HTTP、FTP、SMTP、POP3等应用层的规约,使PLC可直接进入因特网,成为不折不扣的基于Web的PLC;也可使产的PLC挂上以德国Siemens公司为主导的工业以太网ProfiNet。在这次系统控制展览会上,我们就见到Profibus组织(JPO)的展台上展出的通过多种方式挂ProfiNet的PLC,富士电机的MICREX-SX系列PLC、横河电机的FA-M3系列PLC都是直接经由其以太网模块挂ProfiNet的,三菱电机的小Q系列PLC则是通过其RS 232C的模块和外挂的RS 232C/以太网协议转换器(JNVE1型)挂ProfiNet的。
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