By Phil Burgert
Switching from copper wire to fiber, or less often from fiber to copper, presents a number of practical choices.
“The decision to use copper wire or fiber involves several factors,” says Don Lupo, director of process sales and marketing for Acromag. “First and foremost it includes the physical transmission distance.” Lupo notes that copper cable transmission distances are generally limited to 100 m. Transmission distances beyond 100 m require additional switches, fiberoptic cables or possibly wireless communications, he says.
“The secondary reason for switching media would be the presence of severe electrical noise,” says Lupo. “Fiberoptic cable is virtually immune to conducted or induced electrical interference and will create an isolation barrier between two systems or locations.”
A third reason to choose fiberoptic cable involves environmental operating issues, the vendors say. The possibility of water or liquid coming in contact with a broken cable, causing a ground short in communications, is one example that might lead to the use of fiber.
Another reason to convert from fiber to copper is a need to use an existing switch that doesn’t have a fiber port on it, says Steve Bowles, regional sales manager for the southeast for GarrettCom.
“If you’re connecting Building A to Building B and the switches in both buildings do not have fiber ports, the most cost-effective and usually easiest way instead of buying a new switch is to get a media converter to connect the fiber between the two,” he says.
Paul Wacker, industrial communication product manager for Advantech, describes the media converter as working at the physical layer to transparently convert between copper and fiberoptic connections. “Media converters are as simple to install as a patch cable,” he says. “Inserted between the copper and fiber cables, the only other required connection is external power.” He notes that the most popular types of media converters are Ethernet and RS-232/422/485 serial.
With Ethernet, a media converter can be installed almost anywhere on a network, although it is important to recognize equipment compatibility, notes Wacker. “Fiber communication rates are fixed, and it's not possible to use a gigabit (1,000 Mbps) media converter with a Fast Ethernet (100 Mbps) one,” he says. “Also, there are two basic types of fiber: multi-mode, which is less expensive and used for short distances, while single-mode is more expensive but capable of longer distances.”
Most problems with conversion to optical fiber are related to fiber cable handling and installation, adds Wacker, warning that copper-to-fiber conversions for users who have limited experience working with fiber might need help, training or a third-party contractor.
“Like copper cable, fiber has a maximum pulling-load rating, which should not be exceeded during installation,” he says, adding that only strength members and not the fibers should be pulled. “Fiber is very strong when pulled straight but breaks easily when bent too sharply, so care should be taken to not exceed the cable bend radius,” he says.
“This type of fiber typically requires a skilled technician with very specialized equipment to complete the terminations,” says Todd Shadle, Interface-serial and Foundation fieldbus product marketing lead specialist for Phoenix Contact. “Connectors are available for the users to terminate smaller diameter fiber cable, but if the connection is poor in quality, early degradation can result and intermittent communication can be difficult to troubleshoot.” He recommends using a larger diameter fiberoptic cable such as a polymer or hardened clad silica (HCS) product that has connectors specifically designed for end-user termination and consistent quality connections with minimal tools.
Connector types in conversions also are easy to overlook, says Kenneth Workman, product manager at Schweitzer Engineering Laboratories. “It is important to ensure that the specified equipment and cables match in connector type,” he says, adding that one simple solution is to buy bulk cable and terminate it on-site with the necessary connectors.
Another common pitfall can be avoided by paying attention to the type of fiber technology used, he adds. “Many times installation plans are made based on some existing fiber infrastructure, but without information as to whether that fiber is single-mode or multimode,” says Workman. “This information must be known before identifying Ethernet equipment.”
