Best Practices for Networking Automation Computers Automation computers can be anywhere, and do very many things. Modern automation computers are connected to networks that may be connected to other networks throughout the plant, and via TCP/IP to the entire world.
Ethernet to the North and to the South
In most plants, there are actually multiple Ethernet networks. There are the device networks on the plant floor. They connect sensors and fieldbus networks and devices to controllers and connect controllers to area controllers and control systems. There are the area-wide networks that group together device level networks and pass data up to higher level networks and computers, and pass data and instructions down to the device level networks.
These networks need to be capable of handling high traffic loading. Most of them require not just a typical Ethernet router, but an Ethernet Switch, and in many cases, multiple Managed Ethernet Switches to interconnect the controls networks and connect the Control Network to the MES/ERP/Plant enterprise network.
Plant Ethernet systems don’t just carry information to and from the device networks either. Often, plants now have VoIP communications networks that also run on Ethernet, and many plants have video inspection and surveillance systems that are also running on the same or co-existent Ethernet networks that the device networks run on. An automation computer can be used as an HMI or controller/router between networks.
Redundant Networks or Redundant Paths?
Industrial networks need robust architectures. Typically, several LAN switches are connected together in a ring, and the Ethernet devices connect to the ring. Standard Ethernet rings are not a fully redundant topology, and are less robust than is required on the plant floor, in either discrete or process industries.
A fully redundant ring topology protocol is usually available from the switch vendor, such as the dual X-Ring topology from Advantech that provides users with an easy way to establish a redundant Ethernet network with ultra high-speed recovery time less than 10 ms.
Thus, there are two ports, two cables, and duplicated LAN switches with duplicate IP addresses for each Ethernet switch in a truly redundant system. The switch protocols make sure that all the devices on the ring use the same application layer protocol and LAN redundancy mechanisms. This redundant ring topology prevents a single network break from impeding the network path, while permitting "best x of y" voting for synchronization.
Even though the ports, cables and switches are duplicated, this provides the application with certain simplicity, since the redundancy is essentially transparent to the user of the network.
Gigabit or Bust!
High bandwidth applications in the plant has caused a major migration from standard Ethernet (10/100) to Gigabit Ethernet. Gigabit Ethernet, is becoming the standard for network speed. Some of these high bandwidth applications include VoIP communications, wireless backhauls, high bandwidth surveillance video, and machine vision applications.
The burgeoning market for wireless devices in the plant and on the shop floor has already required increased bandwidth from the wireless gateway to the control systems (the backhaul). More and more, plants are concentrating their security systems into the same networks that carry plant data and the VoIP communications network. This, too, is requiring Gigabit Ethernet. AIDC applications like automatic barcode readers and active or passive RFID readers have also increased the required bandwidth on the plant floor. Finally, advanced sorting/control algorithms have been developed for machine vision systems that make them more useful in many applications. It is now necessary for the typical Ethernet switch to be capable of gigabit speeds, as well as robust redundancy.
Legacy Networks/Device Integration -Notwithstanding the huge gains and the standardization, there are still many devices on the plant floor that are not directly able to use Ethernet for communications. Many are serial devices, using RS-232, RS-422, or RS-485 communications. Others use proprietary communications networks, like Modbus, or Profibus or Foundation Fieldbus. Some Modbus devices can connect to an Ethernet LAN using Modbus/TCP protocol. Others need a Modbus-to-Ethernet Gateway.
Serial devices are ubiquitous. They require gateways to be able to connect to an Ethernet LAN. These devices can be field mounted, for to a single device like a barcode scanner, or they can be part of the network architecture in rack or panel configurations.
Profibus and Foundation Fieldbus networks require gateways,except for FF HSE. As wireless networking grows in popularity, wireless network gateways are also being required to connect the wireless sensor networks to the infrastructure.
So what should an "industrial strength" automation computer that is being used as an Ethernet network appliance look like?
They can have many different physical shapes and construction. They can be designed for mounting in the field, such as Advantech’s EKI serial device servers. They can be designed for rack or panel mounting such as Advantech’s UNO embedded automation computers. They can be designed for mounting in Ethernet ring structures, such as Advantech’s EKI Ethernet switches. They need to have industrially-hardened circuit boards. They need to have wider-than-commercial operating temperature specifications. They need to have industrial mounting that prevents damage from shock and vibration. In other words, they need to be as robust and the plant floor devices they are networking.