Industrial networks demand rugged solutions for multiple environments; commercial networks are generally lower-cost but hardware may not suit rugged appliclations. Adapting commercial networks, such as Ethernet, is increasingly popular among users and manufacturers.

Considerations in making network connections include topology, type of hardware needed (see related text on gateways, bridges, routers, switches), media and device information, and the level or levels at which networks can serve.

InterlinkBT (Plymouth, Minn.), a joint venture between Banner Engineering and Turck Inc., specializes in fieldbus-related products. Bob Svacina, marketing director, says Ethernet is the biggest emerging trend, but there's uncertainty. "With a PC or PLC host, it works OK, but device manufacturers are having trouble at the slave level because Ethernet communication chews up a huge amount of real estate on the circuit board, pushing the cost up. To make Ethernet deterministic requires smart switching hubs, which is expensive, perhaps up to $100 per drop. In the office, if a print file messes up, you just send it again, but if a robot goes crazy, a lot of damage can be done."

Hirschmann-USA (Pine Brook, N.J.), which says it's first with a line of industrially hardened Ethernet hardware, has switches, hubs, fiber-optic rail transceivers, and other products. People there say they're just in time, as major PLC manufacturers offer ports to Ethernet.

In October 1998, Hirsch-mann unveiled its Industrial Rail Line Family, a hardened line of Ethernet products, says John McGilvreay, Hirschmann network systems division sales manager for North America. (Parent company is based in Nuertingen, Germany.)

Mr. McGilvreay says Hirschmann's line, unlike commercial products, is DIN-rail mounted, 24 V dc power (rather than 110 V), redundant, and offers link recovery in less than 300 milliseconds. Designed for industrial automation, the products take the heat at 60 °C, without fans. "Customers tell us commercial Ethernet hardware can't last three months in hot, humid, industrial applications."

Mr. McGilvreay says, "With full duplex operation, prioritization and wire speed switching of up to 1 gigabit/sec, Ethernet has become a deterministic Ethernet service.

Proper network design can go a long way toward improving performance, including, for critical applications, a fault-tolerant Ethernet network design. Equipment can't make up for poor design, says Mr. McGilvreay. "You can poorly design an Ethernet network, just like any other network."

Customers want an open system standard, he says. "We're going to see more Ethernet TCP/IP—it lends itself to remote control and management through the Internet. Ethernet also has scalability from 10 megabit, to 100 megabit, to gigabit Ethernet. As demand in-creases, prices will fall, like the commercial

market, where an Ethernet networking card is available for $20 and a five-port hub is under $40." Issues manufacturers need to address include standardizing connectors, network security via firewalls, and establishing a standard application layer, he suggests.

Beyond whether to offer Ethernet or not, device manufacturers have been faced with deciding which industrial networks to support.

SST Division of Woodhead Canada (Waterloo, Ontario) helps by offering the UCS (Universal Communication System), to offload the communications burden from device manufacturers. Using SST's UCS removes the risk of choosing, developing, and maintaining the network interface, allowing device manufacturers to focus on core competencies.

Corina Silberman, product marketing manager, SST Gateway Technologies, adds, "With UCS, when connecting to current and future modules, no code change is required to the host product. This makes UCS unique; other products require code change to the host product. The most viable previous alternatives included integrating one network at a time to a device using a protocol stack." Another SST product, X-Link, provides gateway translations from one network to another, such as between Rockwell Automation/Allen-Bradley Data Highway Plus and Groupe Schneider's Modicon Modbus Plus (photo).

Synergetic Micro Systems Inc. (Downers Grove, Ill.) makes networking life easier via software drivers and fieldbus interface cards for multiple networks. Its set of Universal Software Drivers allows an integrator to build a system around one network, then transfer the investment to the next without making any software changes, according to company president, Michael B. Justice. Synergetic technology partner HMS Fieldbus Systems (Halmstad, Sweden) offers the AnyBus module, an interchangeble OEM fieldbus module for multiple networking applications.

Mr. Justice says, "Synergetic has defined industrial Ethernet as three things: an industrial DB9 connector (following the Siemens and Hirschmann specifications), a product or board that will survive in an industrial environment, and a long-term reliable supplier. These items along with with standard Microsoft Windows driver compatiblity give the industrial user a reliable product at a reasonable cost from a constant source."

Other networking products are becoming more industry specific, such as use of Teflon and stainless steel materials for semiconductor and pharmaceutical industries. Another example is Turck Inc.'s recent MSHA (Mine Safety and Health Administration, U.S. Dept. of Labor) approval for more than 50 industrial-grade cable/connector components (photo). Similarly, Daniel Woodhead Co.'s Brad Harrison (Downers Grove, Ill.) unit has widened its range of sizes and breadth of quick-disconnect networking products.

Topologies, the patterns of interconnections among nodes, also can influence a network's cost and performance. Topologies include bus (linear, branching, and tree), ring, and a combination of bus and ring through gateways, routers, and bridges. Star topology, often used in Ethernet, has a central node connecting to individual nodes. Mesh topology connects each node with every other node. For more about topologies, see Control Engineering, March 1998, p. 198, "Back to Basics" column, "How to Untangle Network Topologies."

Network component manufacturers also can help confirm if the pattern of interconnection among nodes will allow the physical network operate as needed.

The number of devices permitted varies, as does distance and network cycle time. Up-to-date information is available from various network organizations, as well as from hardware vendors and system integrators. Major automation vendors often sell or have partners provide hardware for multiple networks. Most belong to multiple network organizations, which often have membership exceeding 100.

Connect with specific networks at:

• ARCNet,www.arcnet.com;
• AS-Interface (AS-i),www.as-interface.com;
• CANopen (CAN-based bus):www.can-cia.de;
• ControlNet,www.controlnet.org;
• DeviceNet (CAN-based bus),www.odva.org;
• Fieldbus Foundation,www.fieldbus.org;
• Gigabit Ethernet,www.gigabit-ethernet.org;
• HART,www.ccsi.com/hart;
• Interbus,www.interbusclub.com;
• LonWorks,www.lonmark.org;
• Modbus,www.modicon.com/openmbus;
• Profibus-DP, -FMS, -PA,www.profibus.com;
• SERCOS,www.sercos.com;
• Seriplex,www.seriplex.org;
• Smart Distributed System (SDS, based on CAN),www.honeywell.com/sensing/prodinfo/sds; and
• WorldFIP,www.worldfip.org.