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Stable Control Signal Connections in Hostile Industrial Environments

Sept. 10, 2014
For Cabling and Connectors Used Outside the Enclosure, a Different World of Requirements Opens up Compared to Devices That Sit Inside NEMA-Rated Boxes
About the Author
Leslie Gordon is a former Senior Technical Writer on Control, Control Design and Industrial Networking magazines.

When it comes to recent technology advancements or design considerations that have helped ensure stable control signal connections in hostile environments that involve moisture, dust, heat, cold or external exposure, many possibilities come to mind. A few applications might include heavy-duty connectors (HDC) designed for oil and gas pipelines, devices intended to work outside the enclosure, modern insulation displacement connectors (IDC) and certain power supplies.
One example of HDCs for harsh environments comes from devices intended for connecting power between the heaters on exposed oil and gas pipelines that might be located in Canada or the northern U.S., where temperatures can fall to -50 ˚C. A fairly recent innovation is a Weidmüller heat-trace connector, which replaces the traditional junction box method of cable connection. The large connectors mate face-to-face and feature diecast, tin-plated, aluminum construction for high strength and impact resistance. A special coaxial design allows 360˚ plugability, meaning maintenance workers need not spend lots of time lining up the two parts at a certain point before mating them. This is especially important because they're working in such extreme temperatures.

"The technology lets workers connect cables quickly and reliably, which is also important because should a pipeline freeze, it would close everything down," says Heidi Kellum, Weidmüller product manager-North America. "After mating the connectors, the technician pushes down a locking mechanism, which ensures the parts don't separate accidentally due to wind or cold. However, the lock was designed to be released easily using a flat edge screwdriver as a lever when disconnecting is required."

For cabling and connectors used outside the enclosure, a different world of requirements opens up as compared to that for devices that sit inside NEMA-rated boxes, says Nate Owens, industrial field connectivity (IFC) product marketing lead specialist at Phoenix Contact USA. For example, outdoor installations necessitate thinking about the entire system instead of just factors such as temperature, which can be controlled by a heat sink in the cabinet, or vibration, which can be controlled through the use of alternate components.

"A problem that's persisted over the years is that of using typical industrial components, specified to withstand oils and abrasion, and mounting them on the side of heavy-duty outdoor equipment such as cranes, lifts and loaders," Owens says. "The cabling and connectors used in these cases must work in much wider temperature ranges, withstand exposure to ultraviolet light, and stand up to a gamut of more extreme conditions."

Recent advances in this area from Phoenix Contact are factory-molded cables that, unlike typical pin-and-socket connectors that must be assembled, are sealed and just plug into display and control devices onboard construction vehicles, agricultural equipment and forestry machinery. Other cordsets such as M12s and solenoid valve plugs employ corrosion-resistant, stainless steel components, silicone gaskets and UV-resistant cabling to ensure they can withstand extreme outdoor environments.

According to Owens, other improvements can be found in push-in technology for connectors. "This actually has been available for decades, but what's new are key functions like a pushbutton for disconnecting, which is important because it lets users rewire easily," he explains. "The connector has a low insertion force and a high retention force, which makes push-in devices a major player in extreme environments because the retention force is higher than that of a typical spring cage."

IDCs, first developed in the 1960s for 28-gauge, seven-stranded wire, have advanced over the years to target a wide range of industrial, lighting and transportation applications. Intended as an alternative to crimp-to-wire and hard-soldering wires to a PCB, the technology usually provides a reliable, gas-tight, wire-to-board connection in harsh environment applications. "However, this capability depends largely on the contact material," says Tom Anderson, connector product manager, AVX Interconnect. "For example, consider a standard IDC that accepts any size wire between 18 and 24 gauge. Here, the contact material must be fairly soft to compensate for the different wire sizes, so the material tends to stress-relieve over time and temperature."

To address this problem, the company designs IDCs to match each specific wire gauge. In addition, instead of soft 260 brass, the contacts are produced in phosphor bronze, which gives them enough flexibility so they won't cut the wire, while providing a high enough force to ensure a robust connection. According to Anderson, the phosphor bronze option even lets users place solid wires into the connector, and get the same performance as with stranded wire, which is unusual because the technology was always based on stranded wire.

In addition, unlike traditional pin-and-socket connectors, users can push the wire into the IDC and then over-mold or pot the unit without having to worry about the potting or plastic getting into the contact area, Anderson says. "This makes the connectors useful for extreme outdoor applications such as emergency vehicle lighting, where the flashing lights are in the grill or on the vehicle roof, while the wiring or control modules are bolted somewhere under the hood or on a wheel well, and are exposed to extreme temperatures, shocks and vibration."

Lastly, the concept of extreme connectors can even include power supplies. For instance, recent power supplies no longer have screw terminals, nor do they need to be located in a control box. Instead, they mount on the machine in the environment. "Units such as our ‘intelligent' power supply change the way designers must think about putting power on their equipment reliably," says Will Healy, strategic marketing manager at Balluff. "Basically, the power supply has a mini-connector that connects the ac to the device and another mini-connector that connects dc to the device, and then it provides dc power on to the equipment for your automation. The devices' IP67 rating means they can be submerged to 1 meter for 30 minutes and still work well, which is pretty impressive."

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