EDS-208A卡件
EDS-208A卡件,
EDS-208A卡件,
在工业以太网没有到来之前，工控行业的发展可以说是步履维艰，为什么这么说呢，因为在工业以太网之前传统的工控行业是靠串口等低速或者短距离通信设备来通信，这就大大限制了工控设备的互联和监控。那工业以太网的发展现状是怎样的呢？它的前景又在哪呢？
所谓工业以太网，一般来讲是指技术上与商用以太网（即IEEE802.3标准）兼容，但在产品设计时，在材质的选用、产品的强度、适用性以及实时性、可互操作性、可靠性、抗干扰性和本质安全等方面能满足工业现场的需要。【4】
2工业以太网技术发展现状
随着互联网技术的发展与普及推广，Ethernet技术也得到了迅速的发展，Ethernet传输速率的提高和Ethernet交换技术的发展，给解决Ethernet通信的非确定性问题带来了希望，并使Ethernet应用于工业控制领域成为可能。目前工业以太网技术的发展体现在以下几个方面：
2.1通信确定性与实时性
工业控制网络不同于普通数据网络的特点在于它满足控制作用对实时性的要求，即信号传输要足够的快和满足信号的确定性。实时控制往往要求对某些变量的数据准确定时刷新。由于Ethernet采用CSMA/CD碰撞检测方式，网络负荷较大时，网络传输的不确定性不能满足工业控制的实时要求，因此传统以太网技术难以满足控制系统要求准确定时通信的实时性要求，一直被视为非确定性的网络。 然而，以太网与交换式以太网技术的发展，给解决以太网的非确定性问题带来了新的契机，使这一应用成为可能。，Ethernet的通信速率从10M、100M增大到如今的1 000M、10G，在数据吞吐量相同的情况下，通信速率的提高意味着网络负荷的减轻和网络传输延时的减小，即网络碰撞机率大大下降。其次，采用星型网络拓扑结构，交换机将网络划分为若干个网段。Ethernet交换机由于具有数据存储、转发的功能，使各端口之间输入和输出的数据帧能够得到缓冲，不再发生碰撞；同时交换机还可对网络上传输的数据进行过滤，使每个网段内节点间数据的传输只限在本地网段内进行，而不需经过主干网，也不占用其它网段的带宽，从而降低了所有网段和主干网的网络负荷。再次，全双工通信又使得端口间两对双绞线(或两根光纤)上分别同时接收和发送报文帧，也不会发生冲突。因此，采用交换式集线器和全双工通信，可使网络上的冲突域不复存在(全双工通信)，或碰撞机率大大降低(半双工)，因此使Ethernet通信确定性和实时性大大提高。
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