——Ethernet的扩展与进一步容纳Web技术
当前，在所有过程控制领域，最大的发展趋势之一就是Ethernet技术的扩展。PLC也例外，现在，越来越多的PLC供应商开始提供Ethernet接口部件。在最近的几年间，我们已经看到，发展比现有普通小快灵PLC更加强大的PLC是种趋势。Ethernet将会成为PLC的通信标准吗？也许最终结果是这样的，但现在还为时尚早。对于在PLC上提供Ethernet接口将能够解决所有通信问题，人们普遍存在着误解。Ethernet仅仅定义了OSI参考模型底部的几层协议标准，如果上层协议相互之间不能兼容，那么仍然不可能进行相互之间的通信处理。打个比方，这如同一个不懂英语的中国人与一个不懂汉语的美国人之间是不能够通过电话进行对话一样。因此，协议就是设备之间相互通信的语言。 另一方面，前进的步伐已经迈出，我们只有迎着困难而上，为了将Ethernet技术应用到工厂底层的现场过程控制设备中去，ODVA协会为此建立了一套全球性标准技术规范，即Ethernet/IP标准，以便能够解决在实际工作中所遇到的困难。 向Ethernet靠近的一个目的在于通过Internet能够连接到所希望的任何地方。实际上，在一些意想不到的地方，Web服务器正在显露出其应有的威力。几年前，有一些PLC系统已经内藏了Web服务器，这无疑又为PLC系统增加了更多的特点。其他类型的控制设备也正在准备进一步集成Web服务器。例如，Square D公司已经有一个具备Ethernet连接接口的发动机控制中心，并正在准备开发一种内藏Web服务器连接接口的变速装置。
PLC latest develop tendency
——The development of Ethernet with hold Web technology further
At present, on all course controlled fields, one of the greatest development trends is the expansion of Ethernet technology. PLC makes an exception too, now, more and more PLC suppliers begin to offer the interface part of Ethernet. During recent a few years, we have already seen , to develop will be ordinarier and smaller soon than to have now efficacious PLC stronger PLC will be one kind of trends. Will Ethernet become the communication standard of PLC? Perhaps the final result is like this, but still early now. As to the thing that offer Ethernet interface to can solve all communication problems at PLC, people generally misunderstand existing. Ethernet has defined some layers of agreement standards of OSI reference model bottom only, if the agreement of upper levels can not be compatible between each other, is still impossible to carry out the address reason between each other, . hit compare , this do not understand one and Chinese of English like one do not understand American of Chinese between is can not carry out dialogue through telephone like. therefore, agreement is equipment between communicate mutually language.
On the other hand, ongoing step has been steped , we have only in face of difficulty on, for will Ethernet technical application go to , ODVA association into the process control equipment on-the-spot of factory bottom have established therefore a set of globalness standard technical standard, the standard of Ethernet/IP, in order to can solve in actual work meet difficulty.
