By Jim Montague, Executive Editor
Dang. It wasn’t supposed to be this difficult. By now, industrial networks were supposed to be completely interoperable and seamlessly humming along in unison. Users were supposed to be able to plug and play any devices they wished into a safe, secure and totally open network.
Well, reality is having a little bit of trouble catching up to this long-sought and often-over-hyped fantasy. Of course, new components and networks run into legacy devices, twisted-pair fieldbuses collide with point-to-point hardwiring, everyone bumps into Ethernet, enterprise systems stick their noses in, and someone starts talking about wireless. Oh, and plant-floor engineers have running arguments with IT staffers, assuming they’ve ever met or talked to each other at all.
Dissolving Boundaries = Stepping on Toes
The historical niches and silos where each type of industrial network originated and grew up have been dissipating. However, most have emerged only to find they don’t speak the same language and there’s far less interoperability and far more incompatibility than their users expected. Even experts in one protocol or network technology say they don’t know as much as they need to about multi-network interoperability.
So, while there’s no magic bullet, there are hardware bridges and gateways, and even some evidence of growing professional cooperation.
“For now, it’s getting worse because the list of networks keeps expanding, their capabilities are crossing platforms, and many networks are being used for tasks for which they weren’t originally intended,” says Les Haman, regional manager for Matrix Technologies, a CSIA-certified system integrator in Maumee, Ohio.
“Usually, most legacy networks can’t be completely replaced, so they have to be supported during and after retrofits, and so we need to keep building bridges to them.”
For instance, Matrix’s engineers recently integrated and replaced much of a proprietary Square D Synet network at AK Steel’s plant in Middleton, Ohio, with Rockwell Automation’s ControlLogix controls. However, Haman says some parts of the old network had to remain Synet, and so Matrix built bridges to the older protocol using third-party Modbus TCP/IP Ethernet. The overall $60 million renovation included mechanical work, I/O buildings, an off-site fabrication room, a hoist and other equipment.
“All that the mill could afford to do right now was to replace the primary off-gas system and add secondary emission collection vacuums and a monitoring system for EPA compliance,” says Haman. “Luckily, there were enough pieces on the market for us to do a prototype and benchmarks, so this solution could be used in a control environment. However, the rest of the plant was all Square D, including the CT probe, flux delivery system and O2 lance probe, and it would have been prohibitively expensive to update all of them. Plus, there were some risks and scheduling that didn’t make it possible.”
What Matrix needed was a common denominator between Synet and ControlLogix. What it found was a stand-alone, third-party, Ethernet protocol converter that plugged into ControlLogix’s backplanes and could use Modbus TCP/IP to have Synet-based devices talk to the ControlLogix network. Haman says the only other option would have been RS-232 hardwiring, which would have been far too costly.
“We were able to help AK Steel save several million dollars that it would have cost to hardwire or replace many of the legacy systems,” says Haman. “Just doing the design, prototype, benchmark and acceptance test was like a little project in itself. However, it made everyone feel better because it showed us options we hadn’t considered before and let us test the capabilities of the new solution.”
It takes a lot of planning to avoid bumping elbows in an industrial network, explains Haman. “You first have to map all the data-flow requirements, such as the kind of information and whether it’s integers or string-type data,” he says. “You also have to determine update rates depending on how fast you’ll need the data. Next, you need to pick which protocol and platforms to use. Finally, you need to draft an interface design specification that has all these requirements in one document, which can help you get your mind around the whole scope of all the data in your system. This one document can help you see and understand what data needs to go where.”
Going With Gateways
Just as intelligent switching and addressing made Ethernet more deterministic and credible, increasingly intelligent gateways and other modules are being used to translate communications and even aid interoperability between many fieldbuses and other networks.