Fiberoptic, Wireless Connections Require Special Considerations

Fiberoptic, Wireless Raise Hackles: Connecting Machines to Networks or In-Line Systems Can Be Tricky, Depending on the Media

By Mike Bacidore

As machine-automation professionals and their IT counterparts find themselves working together more often, the need for controls engineers to understand newer industrial networking options continues to grow accordingly.

In the February issue's cover story ("Stick to the Playbook," Feb10, p28, www.ControlDesign.com/retainknowhow), a surprising number of designers and builders discussed the inclusion of their machines in in-line systems and on networks.

While copper wire remains the communication standard for physical media, other options such as fiberoptic and wireless technology often make better sense in certain applications. But each bears its own issues. Just the thought of terminating fiberoptic cable can make an engineer's hair stand on end, but connecting wireless access points should raise hackles just as often.

Wireless or radio networks have their advantages and disadvantages, says Joe Roegner, SCADA technician for Orange County (orangecountyfl.net) in Orlando, Fla. "Issues range from security to the potential of widespread communication loss from failure of an access point," he says. "But this has great potential as the technology matures. Keep an eye on how these systems perform under stress, such as during hurricane conditions. Many cell-phone networks had problems during the 2004 hurricane in Florida. To be fair, a spread-spectrum radio system did not do very well as power losses covered most of the territory."

When executed properly with suitable technology, wireless access points have little impact on reliability, says Charlie Norz, product manager—Wago-I/O-System, Wago (www.wago.com). "Advanced Bluetooth transceiver modules, for example, monitor and proactively report signal strength," he explains. "This provides assurance that data is being processed securely and can alert engineers if signal strength begins to degrade. Of course, wireless networking has other benefits."

Norz cites the lower networking costs that wireless creates by minimizing the amount of materials such as cable or conduit and the number of labor hours required to design, route and secure network cabling. "It also provides greater freedom and flexibility when networking widely spaced machines or plant floors with machines at different elevations or levels," says Norz.

"Adding wireless access points into a network makes it easier to access the system for troubleshooting and tweaking settings, which can help make startup go smoothly," adds Sven Burkard, product manager, Belden, Hirschmann & Lumberg Automation (www.belden.com). "However, there are some issues to look out for. Improper network configuration can cause excessive data to propagate across the wireless link, which affects reliability. If there's more than one access point, it's also possible to create network loops if the devices aren't configured properly. But these are all issues that should be detected during a network validation and test."

As mentioned previously, fiberoptic cables also have their downsides, especially when it comes to termination. Cables with preinstalled connectors are available, but while these eliminate the complications of terminating fiberoptics, they also create a need to know cable lengths with a very small margin of error.

"When we can control and measure the lengths relatively well, we'll go with the preinstalled connectors," says Tom Prokop, manager of infrastructure and remote services, Consol Energy (www.consolenergy.com), Pittsburgh. "You have to use a little more care when you're pulling them through, but all of those tend to be assembled in a quality-controlled environment, and they're ship-protected. We've looked at all kinds of different connectors. A lot really depends on how well you can control the dust in the environment and what type of cable you're working on."

Molex's Chris Zimmerman suggests using field-installable fiberoptic connectors initially to lay out the prototype system. "Once the system has been laid out and tested, the fiberoptic lengths can be finalized, and then factory-terminated or predetermined length cables can be purchased," says Zimmerman. "This is the best advice for production systems, rather than one-off or custom systems."

Although pre-terminated fiberoptic cables are thought to reduce the likelihood of complications during installation, such practices actually can cause more harm than good, explains Burkard. "Long fiber runs of more than 50 ft should allow for a few feet of slack and should be field-terminated and connected to a fiber patch panel, with a short fiber patch cord completing the connection to the end device," he says. "This reduces the possibility of miscalculating length or damaging the connectors during the installation or pulling of the fiber. The patch panel also lets the user easily change end devices without concern for the fiber connector type. A simple change in the patch cord will resolve this."

Additionally, if a facility's use of fiber is growing significantly, it's best not to rely solely on a contractor or specialist for fiber termination. "In-house expertise is easy to achieve by taking one of the many certification classes offered and investing in a quality fiber termination tool kit," says Burkard.

By using fiberoptics only where they're best suited—to traverse long distances or connect different buildings thereby eliminating the issue of different ground potentials—you'll eliminate many of the variables for getting the right lengths, explains Nick Clute, product specialist at Turck (www.turck.com). "Generally, if you're running long distances, you have known measurements that can be easily estimated," he says. "There's only one place to connect, in the server room, and there's a predefined switch cabinet out on the floor. The thing to remember is these cabinets can't change, so just make sure you get close enough to the final installation that copper can be run from there. Beyond that, it's easy to hide extra cable by adding slack to the line between mounting points and using a service loop at varying intervals to take up some slack."

The same techniques that were used to create copper-connectorized solutions can be used with fiber, as well, says Clute. "Keep in mind are the maximum pressure you can put on the cable with a zip tie and the minimum bend radius," he says. "If you keep those two specs of the cable in mind, everything will be fine."

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