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PLC及其网络发展到现在,已经能够实现NBS或ISO模型要求的大部分功能,至少可以实现4级以下NBS模型或ISO模型功能。 PLC要提供金字塔功能或者说要实现NBS或ISO模型要求的功能,采用单层子网显然是不行的。因为不同层所实现的功能不同,所承担的任务的性质不同,导致它们对通信的要求也就不一样。在上层所传送的主要是些生产管理信息,通信报文长,每次传输的信息量大,要求通信的范围也比较广,但对通信实时性的要求却不高。而在底层传送的主要是些过程数据及控制命令,报文不长,每次通信量不大,通信距离也比较近,但对实时性及可靠性的要求却比较高。中间层对通信的要求正好居于两者之间。 由于各层对通信的要求相差甚远,如果采用单级子网,只配置一种通信协议,势必顾此失彼,无法满足所有各层对通信的要求。只有采用多级通信子网,构成复合型拓扑结构,在不同级别的子网中配置不同的通信协议,才能满足各层对通信的不同要求。 PLC网络的分级与生产金字塔的分层不是—一对应的关系,相邻几层的功能,若对通信要求相近,则可合并,由一级子网去实现。采用多级复合结构不仅使通信具有适应性,而且具有良好的可扩展性,用户可以根据投资情况及生产的发展,从单台PLC到网络、从底层向高层逐步扩展。下面列举几个有代表性公司的PLC网络结构。 三菱公司的PLC网络 三菱公司PLC网络继承了传统使用的MELSEC网络,并使其在性能、功能、使用简便等方面更胜一筹。Q系列PLC提供层次清晰的三层网络,针对各种用途提供较合适的网络产品,如图7-24所示。 图7-24 三菱公司的PLC网络 (1)信息层/Ethernet(以太网) 信息层为网络系统中较高层,主要是在PLC、设备控制器以及生产管理用PC之间传输生产管理信息、质量管理信息及设备的运转情况等数据,信息层使用较普遍的Ethernet。它不仅能够连接windows系统的PC、UNIX系统的工作站等,而且还能连接各种FA设备。Q系列PLC系列的Ethernet模块具有了日益普及的因特网电子邮件收发功能,使用户无论在世界的任何地方都可以方便地收发生产信息邮件,构筑远程监视管理系统。同时,利用因特网的FTP服务器功能及MELSEC**协议可以很容易的实现程序的上传/下载和信息的传输。 (2)控制层/MELSECNET/10(H) 是整个网络系统的中间层,在是PLC、CNC等控制设备之间方便且高速地进行处理数据互传的控制网络。作为MELSEC控制网络的MELSECNET/10,以它良好的实时性、简单的网络设定、无程序的网络数据共享概念,以及冗余回路等特点获得了很高的市场评价,被采用的设备台数在日本达到较高,在世界上也是**的。而MELSECNET/H不仅继承了MELSECNET/10优秀的特点,还使网络的实时性更好,数据容量更大,进一步适应市场的需要。但目前MELSECNET/H只有Q系列 PLC才可使用。 (3)设备层/现场总线CC-Link 设备层是把PLC等控制设备和传感器以及驱动设备连接起来的现场网络,为整个网络系统较低层的网络。采用CC-Link现场总线连接,布线数量大大减少,提高了系统可维护性。而且,不只是ON/OFF等开关量的数据,还可连接ID系统、条形码阅读器、变频器、人机界面等智能化设备,从完成各种数据的通信,到终端生产信息的管理均可实现,加上对机器动作状态的集中管理,使维修保养的工作效率也大有提高。在Q系列PLC中使用,CC-Link的功能更好,而且使用更简便。 在三菱的PLC网络中进行通信时,不会感觉到有网络种类的差别和间断,可进行跨网络间的数据通信和程序的远程监控、修改、调试等工作,而*考虑网络的层次和类型。 MELSECNET/H和CC-Link使用循环通信的方式,周期性自动地收发信息,不需要专门的数据通信程序,只需简单的参数设定即可。MELSECNET/H和CC-Link是使用广播方式进行循环通信发送和接收的,这样就可做到网络上的数据共享。 对于Q系列PLC使用的Ethernet、MELSECNET/H、CC-Link网络,可以在GX Developer软件画面上设定网络参数以及各种功能,简单方便。 另外,Q系列PLC除了拥有上面所提到的网络之外,还可支持 PROFIBUS、Modbus、DeviceNet、ASi等其它厂商的网络,还可进行 RS-232/RS-422/RS-485等串行通信,通过数据专线、电话线进行数据传送等多种通信方式。 主营产品:Schneider ,Foxboro,Ovatin,Allen-Bradley,Siemens等各类工控产品, 欢迎来电咨询! ★厦门市海沧区沧虹东路12号2002室★ **疯狂较低价 EATON CORPORATION SVX050A14A1N1 USPP SVX050A14A1N1 EATON CORPORATION 91-00745-02 USPP 910074502 EATON CORPORATION 92-00804-02 USPP 920080402 EATON CORPORATION 92-01227-00 USPP 920122700 EATON CORPORATION CB000025030 FNFP CB000025030 EATON CORPORATION 91-00745-04 USPP 910074504 1 EATON CORPORATION DYNAMATIC 158672 DRIVER BOARD N1-1 EATON CORPORATION 92-01262-00 USPP 920126200 NEW EATON CORPORATION DYNAMATIC 15-886-5 PCB BOARD FOR AF5000+VFD 7500XE EPRO EATON CORPORATION CUTLER HAMMER OPERATOR INTERFACE PC EATON CORPORATION ECN1611EAA USPP ECN1611EAA EATON CORPORATION A10EN0A NSPP A10EN0A EATON CORPORATION C80DG221N00-B-?103 USPP C80DG221N00B10?3 EATON CORPORATION 6300835 FNFP 6300835 EATON CORPORATION A10EN0A USPP A10EN0A EATON CORPORATION A10EN0C USPP A10EN0C EATON CORPORATION 92-00802-00 USPP 920080200 EATON CORPORATION C361SF264 NSPP C361SF264 EATON CORPORATION DYNAMATIC 15-46-14 CONTROL BOARD 70-47-316, 154614 EATON CORPORATION 92-00804-02 USPP 920080402 EATON CORPORATION 91-00996-00 USPP 910099600 EATON CORPORATION D26MRD-402A1 USPP D26MRD402A1 EATON CORPORATION UVC1000 USPP UVC1000 EATON CORPORATION 10250T-4341 NSFP 10250T4341 EATON CORPORATION PCC-0030H USPP PCC0030H New EATON Corporation Vickers MCV5-10-C-A-10?0-12T-25/ Eaton Corporation PW9355 transforming 1024025-A EATON CORPORATION 92-01039-00-09?-00285 USPP 92010390009002?85 EATON CORPORATION XTSC025DCA NSFP XTSC025DCA Eaton Corporation CH42B200KP Main Breaker Load Center EATON CORPORATION E50-ANS3 NSFP E50ANS3 EATON CORPORATION POWERWARE 5125 15OOi TOWER EATON CORPORATION 5115 NSFP 5115 Eaton Corporation Time Lock 120hr dual movement Eaton Corporation Cutler Hammer Current Transformer Sensor #7801C40G01 Eaton Corporation Pulsar 68180 EX 700 Tower 230V Dual Conversion Online UPS!! 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