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| 型号 |
PM825-1 |
类型 |
DCS |
| 加工定制 |
否 |
是否进口 |
是 |
有几种不同类型的 Data Highway 网络:Data Highway (DH)、Data Highway Plus (DH+)、Data Highway II (DHII) 和 Data Highway-485 (DH485)。DH 和 DH+ 是相似的,因为它们使用相同类型的物理介质和构造原理。DH和DH+的主要区别在于通信方式。DHII 使用同轴电缆,而 DH 和 DH+ 使用双轴电缆。虽然这两种电缆都用于数据传输,但同轴电缆电缆在远距离提供更好的噪声保护,而双轴更适合短距离高频应用。DH485 使用支持 RS485 通讯协议的电缆。在所有数据高速公路中,您最可能看到的是 DH+ 网络。更深入的信息,包括网络布线说明,可以在 Allen-Bradley 数据高速公路安装手册中找到。
在我职业生涯中维护的几乎所有 2000 年之前建造的工业设施中,我都在内部某处看到了 DH+ 网络。我一直是以太网网络的支持者,但我不能忽视 DH+ 网络的一些明显优势。
让我们先回顾一下网络是如何通信的。每个联网设备称为一个单独的“节点”。每个节点都必须有自己的编号,以便与其他设备区分开来。DH 使用一个名为 Floating Master 的系统将数据发送到其他节点。这允许关键节点比其他节点更快地进入网络。所有其他版本,DH+、DHII 和 DH485,都使用令牌传递。这是一个系统,在其中一个节点完成其数据后,它会将优先级移交给队列中的下一个节点。
与现代网络相比,DH 网络上的数据速率相对较慢,但这可以通过较短的数据包来解决。在整个计算机网络中,这个“数据包”是对地址、配置和设备之间发送的实际数据位的集合的术语。随着网络中节点数量的增加,每个设备的连续读数之间的时间将会增加。在许多必须要求安全或即时响应的系统中,应认真考虑此时间延迟。在大多数情况下,可以提高数据传输速率,但通常以减少电缆长度为代价。
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There are several different kinds of Data Highway networks: Data Highway (DH), Data Highway Plus (DH+), Data Highway II (DHII), and Data Highway-485 (DH485). DH and DH+ are similar because they use the same type of physical media and construction principles. The main difference between DH and DH+ is the communication method. DHII utilizes coaxial cable, while DH and DH+ utilize twinaxial cable. While both types of cable are used for data transmission, coaxial cable offers better noise protection at long distances, while twinaxial is better suited for short-range high-frequency applications. DH485 uses a cable that supports the RS485 communication protocol. Of all the Data Highways, the one you are likely to see most is the DH+ network. More in-depth information, including network wiring instructions, can be found in the Allen-Bradley Data Highway Installation Manual.
In nearly every industrial facility built before 2000 that I have maintained in my career, I have seen a DH+ network somewhere inside. I have always been a proponent of ethernet networks, but I cannot discount some distinct advantages of the DH+ network.
Let's start by going over how the networks communicate. Each networked device is called an individual ‘node’. Each node must have its own number so that it can be differentiated from other devices. DH uses a system called Floating Master to send out data to the other nodes. This allows critical nodes to get onto the network more quickly than others. All other versions, DH+, DHII, and DH485, use token passing. This is a system in which, after one node finishes with its data, it hands priority off to the next highest node in line.
The data rate on a DH network is relatively slow compared to modern networks, but this is countered with shorter data packets. Throughout computer networking, this ‘packet’ is the term for the collection of address, configuration, and actual data bits that are sent between devices. As the number of nodes in a network increases, the time between consecutive readings of each device will increase. This time delay should be seriously considered in many systems where safety or instant response must be required. The rate of data transmission can be increased in most cases, but often at the expense of decreasing maximum cable lengths.