Migrating industrial networks
Sooner or later, that legacy plant-floor network must be upgraded. When that time comes, control engineers should use network migration best practices.
While your trusted plant-floor network may have served you well these many years, there will come a time when you need to think about upgrading. Perhaps the benefits of a modern industrial network are just too great to ignore, or the scarcity of parts to keep things up and running is becoming a real challenge. Whatever the reason, the benefits of upgrading can be significant. So can the challenges. No worries, others have been there before you. Here is what you need to know.
Then and now
Not so long ago, all industrial networks were mainly proprietary creatures. Control devices were largely hardwired. Information crawled along at relatively low speeds, and network topologies came in a variety of configurations. Plant-floor data storage and analysis was relatively limited. Network cabling media was largely copper and, more often than not, installed by an electrician versus a network cabling firm. It was not uncommon to have multiple networks comingled on the same plant floor.
There were many proprietary industrial communication networks in this earlier era including DH1, DH, and DH+; Modbus RTU; TIWAY; and many more. Each controller manufacturer also had at least one proprietary device-control I/O network, sometimes more, depending on the variety of makes and models they offered. Networks were largely deterministic at the time, particularly I/O networks.
Today, plant-floor devices continue to get smarter, providing remote configuration, calibration, and diagnostic capabilities only dreamed of a short time ago. The cost of both bandwidth and storage continue to plummet, allowing for plant-floor data warehousing and analytics on a scale not previously possible. Industrial Ethernet in its various forms is beginning to dominate manufacturing networks globally as the solution platform of choice. It's a communications network, it's a fieldbus, and it's highly interoperable.
Information analysis from the plant floor and across the enterprise is becoming an essential and standard part of most modern control systems. While the benefits of this information explosion can result in significant boosts to the efficiency and quality of a manufacturing process, it comes at a cost. There are new challenges with the physical media installation, network equipment configuration, system security, and more that you are likely to encounter when upgrading to a modern industrial network platform. Let's take a closer look at some of the issues you might encounter along the way and how best to handle them.
Plan to succeed
A solid network migration plan is the foundation for a successful outcome. It begins with a good understanding of where you are and where you want to be. Start with a comprehensive system architecture drawing of your new industrial network. It should include all devices and switches connected to the network, references to their name and physical location, cable type references, and intended IP addresses listed throughout.
Next up is documenting your existing network. You may need to do a bit of detective work to identify all connected devices, ascertain their logical network address, and their physical locations. You also have to document the physical cable type and wiring configuration on the network. You may encounter trunkline/dropline configurations, daisy chained wiring, or other configurations. Each of these legacy networks has very specific cabling, shielding, and connection best practices. This information is generally readily available online or from the manufacturer.
Some of these older networks are very sensitive to the amount of information moving across them and the amount of devices connecting to them. If you are phasing in installation and you need to connect to an existing network, simply adding one more connection may bring the entire network to a halt. You will need to take a close look at both node count and traffic on these older networks before attempting to integrate with them. Trapping and counting communication error codes in your controller can give an early warning if there might be a problem in this regard and help you plan accordingly.
Speaking of error codes, there is another issue that may occasionally surface. It occurs when a modern processor or I/O scanner is upgraded and the legacy network remains otherwise intact. With improvements in technology over the years, these newer devices may be more sensitive to network communication failures than their older counterparts. Errors that were previously too transient or invisible to the older processors just might be picked up by their modern cousins. If you find yourself in this position, you may need to kick back to the older processor as you work your way through the issue. A thorough review of the best practices of your legacy platform is generally the best path toward identifying the source of the problem.
After you have documented your new network, thoroughly researched your existing one, and vetted any potential points of failure, you can put together your detailed plan on how to migrate from one platform to the other. Now let's take a closer look at some of the requirements of a modern industrial network.
Like all networks, your industrial Ethernet is only as good as its cabling (see Figure 1). Industrial applications are often electrically noisy places. They are subject to high electromagnetic interference (EMI), wide temperature ranges, dust, humidity, and a host of other factors. The ANSI/TIA-1005 standard states that Category 6 or better cabling should be used for hosts or devices that are exposed to an industrial environment. Category 6 cable is good for up to 1 GB at 100 meters (328 ft) and 10 GB at 55 meters (180 ft). Category 6e cable can support up to 10 GB at 100 meters (328 ft).
Category 6/6e cable is generally less susceptible to cross talk and external EMI noise. Versions are available that are less susceptible to physical deterioration in the harsher industrial environments. Make sure that the RJ45 ends and jacks are also rated for Category 6. For the best results, use premade patch cables for short runs, with factory installed connectors. For long runs you will need to install jacks.
Shielded Ethernet cable may perform better in high EMI environments if run outside of conduit. You need to install this properly, or it will create more problems than it solves. The key to the use of a shielded cable is in proper grounding.
A single ground reference is essential. Multiple ground connections can cause what is referred to as ground loops, where the difference in voltage potential at the ground connections can induce noise on the cable. This can wreak havoc on your network. To get this right, use a grounded RJ45 connector on one end only of the cable. On the other end use a nonconductive RJ45 connector to eliminate the possibility of ground loops.
If your Ethernet cable crosses power lines, do so at right angles. Separate parallel Ethernet and power cables by at least 8 to 12 in. with more distance for higher voltages and longer parallel runs. If the Ethernet cable is in a metal pathway or conduit, each section of the pathway or conduit must be bonded to the adjacent section such that it has electrical continuity along it entire path.
In general, route Ethernet cables away from equipment that generates EMI. This includes things like motors, motor control equipment, lighting, and power conductors. Within panels, separate Ethernet cables from conductors by at least 2 in. When routing away from EMI sources within a panel, follow the recommend bend radius for the cable.
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