By Mike Bacidore, Managing Editor
Connectors are the glue that holds an industrial network together. Whether you rely on fiberoptic cable, copper cable or wireless communications, the connectors you choose will have a profound effect on the reliability and dependability of your network. And the environment can dictate which type of connectors is the best fit.
"Our biggest industrial environments have the same three problems—dust, vibration and water," explains Tom Prokop, manager of infrastructure and remote services, Consol Energy (www.consolenergy.com), Pittsburgh, Pa., which uses primarily fiberoptic cable at its sites. "If we know it's a high-vibration environment, we find connectors with good mechanical locks on them. We tend to migrate more to an SC barrel connector on our fiber, rather than an SC connector that might just slide in. For the electrical side, we look for things we can mechanically fasten. We use a mix of fiber and copper. All our backbones are fiber. That can be about 70-80% of our cable. Typical fiber runs might be a mile to 12 miles. In terms of connectors, it's probably 50-60% fiber."
Joe Roegner, SCADA technician for Orange County (orangecountyfl.net) in Orlando, Fla., sees similarities between his water and wastewater treatment environment and the wiring done on sea vessels. "With an ocean-going ship, vibration and corrosion are common, so using things like butt connectors to join wires are taboo, while ring connectors for terminations are preferred," he explains.
Alice McWilliams, PE, senior instrument and controls engineer at Chevron Phillips (www.cpchem.com) in Pasadena, Texas, thinks high-vibration environments are one of the more difficult environments to handle. "They can cause connections that intermittently are bad," she says. "When the connection is good 95% of the time, it's very hard to find the source of the problem."
Any environment with harsh temperature, vibration or moisture conditions could potentially cause issues, warns Matt Finlinson, sales engineer at Molex (www.molex.com). "Choosing connections that have proper IP ratings to guard against dust and water is essential," he says. "For instance, in a factory setting, these connections might be subject to machine washdown."
Even a small amount of contaminants has the potential to cause havoc in networks if the connectors are not properly sealed, cautions Nick Clute, product specialist at Turck (www.turck.com). "Any sort of mechanical disturbance—for example, high vibration—can cause network issues in regard to the connectors," he says. "But it may not be clear to all users why an IP67-rated M12 connector should be used instead of a standard RJ45 IP20-rated connector for Ethernet in a standard manufacturing environment."
The three main culprits are vibration, temperature cycling and corrosive gases, summarizes Michelle Goeman, product manager—terminal blocks and electronic interface, Wago (www.wago.com). "Applications and environments prone to severe or extended vibration are among the most problematic, especially for screw terminations," she explains (Figure 1). "In industrial settings, we've seen failed control panel connections halt production. A shift's worth of time and productivity are lost to a 30-cent screw terminal. As machinery ramp up, they create vibrations that may cause screws to back out—hence, the need for extensive preventive maintenance programs, where lines are idled so connections can be checked either with thermal imaging technology, which is expensive, or retorquing to spec, which is time-consuming."
Industrial applications subjected to temperature cycling also trigger connection failures, explains Goeman. "Beyond current-induced changes, consider the environment," she advises. "Factory floors quickly heat up and quickly cool; in industrial settings this leads to changes of hundreds of degrees. All of this causes copper conductors—the most basic, yet important, part of control systems—to expand or contract, and this is on top of current-induced changes. If the interconnect device, such as a terminal block or simple splice, doesn't compensate for this, the connection may fail. Sulfur, nitrogen, chloric gases and even salt oversprays also significantly degrade connections. This is where connection material and a gas-tight connection become vital to network reliability."
Test the Network
Network validation tools are available to test point-to-point and end-to-end runs, but knowing when to use what and whom to trust can be the trickiest part of validating the system.
"Several years ago, our construction contractor made the connections that assembled the communication network for our DCS highway," recalls Chevron Phillips' McWilliams. "After startup, we began to experience communication problems on both the active and redundant highways. When the connectors were examined, they were so misshapen that it became very apparent the wrong tools had been used. We then contacted the DCS company and asked them to check and repair our highway. However, this was only after we had experienced a lot of tense moments concerning our communication between the DCS consoles and the DCS controllers. It would have been better to use the correct contractor the first time. The situation could have been taken care of before startup if we had thought to inspect these connections as part of a startup checklist instead of taking for granted that they had been correctly put together."