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.

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 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).

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