Control Platforms: Network Strategies

Given the state-of-the-art for industrial Ethernet, the future of its use over that of fiberoptic is bright as demand for industrial control LAN capacity grows. By Managing Editor Steve Kuehn.

 By Steve Kuehn, Managing Editor

Seeking greater bandwidth, integration, interoperability and reliability, control network designers increasingly turn to Ethernet to connect industrial control systems across the plant floor. Deploying control-level and device-level networks via Ethernet also provides the means to deliver factory floor data up the organization for consumption by enterprise resource planning (ERP) and manufacturing execution systems (MES). Over the past five to 10 years, Ethernet has become an industrial protocol of choice.

Given the state-of-the-art for industrial Ethernet (100 Mbps, full duplex in a switched architecture), network latency and other data reliability issues have mostly been addressed. That is, until you butt up against the physical limitations of copper wire-based Ethernet cabling. Featuring four twisted pairs of unshielded copper wire (UTP), typical CAT5 Ethernet cable is vulnerable to signal degradation over long distances (limited to about 100 m) and subject to radio frequency and electromagnetic interference (RFI and EMI).

Network Architects See the Light
To overcome CAT5 performance issues in the industrial setting, network architects have an extremely viable option in fiberoptics. Fiberoptic cabling or, for this discussion, Ethernet over fiberoptic local area and wide area (LAN and WAN) networks, can provide manufacturers and processors with an industrial-strength plant and enterprise-wide data highway with essentially limitless capacity.

            RACK 'EM UP 
             
           

In an industrial setting, one is likely to encounter high-speed Ethernet data networks that interconnect fiberoptic cabling with copper CAT5 cabling. Switching and converter technologies, like the gear shown racked here, let system architects create reliable, integrated networks. Source: Saber Engineering



"Fiber's bandwidth is essentially infinite," says Frank Madren, president of GarrettCom, a maker of industrial fiberoptic switching and signal-converting technology. "Fiber media is an ideal enabling technology for extending Ethernet into industrial environments." Madren points out that most of the objections to fiberoptics--those associated with cost and installation--have been mitigated by cable suppliers and the companies that do network installations (see Sidebar Story at the bottom of this article).

Actually, for industrial control and device level LANs and WANs, it appears the most cost-efficient, reliable and high-performance network is comprised of a combination of fiber and copper media, deploying copper media in short runs and fiber as the heavy data-lifting backbone to cover distances and protect signals from noise.

To manage signal conversion across the cabling media, architects rely on managed switching or transceiver technologies that terminate the fiber and provide multiple RJ45 ports. Madren explains that while fiber is capable of supporting bandwidths greater than the 1-Gb limit for copper, switches are bandwidth-specific and generally come in 10 Mb, 100 Mb and 1 Gb speeds. Considering that 10 Mb (common for copper Ethernet) is some 200 times faster than traditional serial network data speeds, even at the low end, switches do not present network architects with data bottlenecks.

Regardless, savvy network architects are turning to fiber media, industrial-strength switches and copper based Ethernet to create LANs and WANs that solve knotty technical and reliability issues on the plant or industrial floor. Such networks have been proven robust, ready and able to deliver control and other device data no matter what bandwidth they require or harsh the environment they're placed in.

Utilities Early Adapters Naturally
Given that utilities often have facilities dispersed across a given geographic area (e.g., power utility with several substations) it's little wonder those types of facilities were early adopters of Ethernet over fiber-optic switched network architectures. But the process control and field device technologies employed by utilities are common to many industrial production environments and it's in this setting that fiber and its associated switch technologies cut their teeth over the years--moving from the commercial (office) realm to the industrial arena, improving their economics along the way.

The City of Sacramento's municipal water treatment system is a good example. Providing the city potable drinking water for decades, in 1998 the City of Sacramento Department of Utilities (CSDU) looked to increase its Sacramento River and E.A. Fairbairn water treatment plants overall capacity nearly 60% and bring elements of each plant into environmental regulatory compliance.

In developing its upgrade plan, CSDU engineers chose to update its networking system. One goal set out by CSDU was that the new network had to be state-of-the-art and able to integrate any future control or monitoring upgrades.

CSDU contracted with Saber Engineering for control system design and implementation. The network Saber Engineering designed was based on a redundant-ring topology using fiber media to support the distances spanning the various supervisory control and data acquisition (SCADA) systems located at the individual treatment facilities located throughout the City of Sacramento (Click the Download Now button at the bottom of this article to view a chart of Sacramento River's fiberoptic network).

Among other things, CSDU wanted to take advantage of fiberoptic's EMI noise immunity to boost the operating reliability of the network. To stretch its upgrade buck, local devices, and computers were connected via copper cabling.

To manage switching duties at the facility level and the systems operations center, fiber switches from Garrettcom were deployed at each main point across the network. "Switches are installed where control points are exercised," says Saber Engineering network designer Brian Thomas. Reinforcing the notion that fiberoptic switchgear has come a long way, he notes that, because of their inherent ruggedness, industrial network designers no longer have to worry about reliability.

"Switch designers have integrated components such as converters, reduced footprints and engineered-out points of failure," say Thomas, "while introducing self-diagnostics and other network reliability-enhancing features." This, in his view, legitimized switches for industrial purposes. "Switches now are well-hardened and can withstand harsh environmental conditions from extremes in vibration, temperature and moisture."

To ensure network reliability in the ring portion of the Sacramento network, Saber installed a Garrettcom S-Ring redundancy manager, based on IEEE's 802.1d spanning-tree protocol standard. The management feature of the fiber switches lets CSDU engineers monitor the health of SCADA network as well as the health of the network at each facility and eliminated the need for a dedicated computer to monitor network health.

Meanwhile in Missouri
The City of Springfield, Mo., faced similar problems but on a broader scale that deployed fiberoptic cabling among treatment process points throughout its Southwest Wastewater Treatment Plant complex. Only two buildings of the nine-building site had in-plant networks and none of them were interconnected. In addition, there was no link between the Southwest facility and the City's Northwest plant.

The objective was to create a network that incorporated existing equipment and ensured that expandable technology was available for future growth. Fiber was chosen because it was easier to deploy throughout the plant and offered immunity to EMI/RFI. It also offered network systems integrator R.E. Pedrotti Co. relief from one more thing: ground current loops.

"Nature is not kind," says Garrettcom's Madren. "Across any given industrial terrain there can be small differences in ground potential that cause ground loops. With fiber's non-conductivity characteristics, ground loops become a non-issue."

Because of the extensive list of legacy equipment involved, Pedrotti deployed Garrettcom converter switches at numerous control points throughout the plant and treatment segments and connected them via fiber cabling to 16-port managed switches. (Click the Download Now button at the bottom of this article to view the chart of Southwest Plant's fibreoptic network.)

Pedrotti used the per-port assignment feature to configure each link according to bandwidth needs and to permit PLC and other device upgrades as needed. An eight-port 10/100 Mb personal switch was installed in the complex's centrifuge building to connect it to the network and another switch was installed at the Northwest plant to provide a fiber uplink via ISDN line to the Southwest plant to complete facility interconnections.

Fiber in Your Future
Both Saber Engineering's Thomas and Garrettcom's Madren agree that the demand for bandwidth in industrial settings is going to grow in the coming years and that fiber-media-based networks now have what it takes to ensure its available when people need it. "With security becoming a much greater issue, it's not hard to imagine companies wanting to deploy video surveillance equipment throughout the plant and use their networks to carry the digital signal," says Thomas. "But there is no bigger bandwidth hog out there than video. If a company wants to deploy real-time video surveillance, fiberoptics is the only way to go." Considering that video requires roughly 5 Mb of bandwidth to support one uncompressed, picture-quality, full-motion video image data stream, a 100-Mb Ethernet environment is the only way to go.

Although fiber's deployment across the manufacturing or process plant floor is, at present, more the exception rather than the rule, just like Ethernet, it's application potential has moved from experimental to practical. Considering that fiber does away with troubling signal reliability issues and has matured to the point where it is no longer the fragile denizen of cushy corporate and pampered telecom LANs, its future is bright as an industrial network medium.

 


Fiber's Cost Model Changing

 

The comparative cost of fiber vs. UTP copper may need to be re-examined. A recent analysis of the installation costs of copper compared to fiber showed surprisingly little difference. In a three-year study by the Fiberoptics LAN Section (FOLS) of the Telecommunications Industry Assoc. (TIA) and Pearson Technologies first installations for copper and fiber were found to be about equal. To access the report visit the FOLS web site: www.fols.org/resources/costmodel_reg.cfm.

(Click the Download Now button below to view the two charts mentioned in this article.)