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Media converters bridge the gap: combined with fiber-optic cabling, devices help solve legacy issues in industrial environments.

Industrial or hardened environments face the challenge of creating interoperability throughout a network in less than ideal environmental conditions. Network administrators in industrial environments are challenged to ensure network performance in harsh outdoor and factory floor locations subject to environmental factors that would render standard, office-grade equipment useless.

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In industrial environments, a wider suite of application-specific, proprietary and legacy serial protocols exists, tying equipment such as programmable logic controllers (PLCs) and process-control instrumentation to man-machine interface terminals. Much industrial equipment with these legacy interfaces cannot be replaced or is too cost-prohibitive to do so.

Fiber offers multiple benefits, including extending the network to the factory floor over long distance, providing signal immunity to electrical noise, future-proofing the network with extra bandwidth and decreasing bulky cable runs. Because of the single connection utility of media converters, fiber does not have to be an expensive all-or-nothing proposition. Deploying fiber through the use of media converters and/or fiber/copper switches allows the adoption of a surgical approach to evolving the network, maintaining the existing plant as much as possible.

Newer network equipment such as voiceover-IP phones, network cameras and wireless access points are often compatible with the IEEE 802.3af power-over-Ethernet (POE) specification. This means the equipment receives its power via the same Ethernet cable used to transport data.

Although this approach saves costs by eliminating separate power cables to network devices, the standard is still limited to the 100-meter (328 feet) distance as standard copper Ethernet cable. When a network-powered device is located outdoors or a long distance away, fiber-based PoE media converters can be deployed near the device, providing the data and power over copper to the device, while extending the network through their fiber ports.

Industrial machines generate large electrical transients and vibration. In a manufacturing or process plant, the air may be dry, humid, dusty or filled with chemical vapors or contaminants. Network components and cabling located outdoors should be moisture-proof or enclosed in NEMA-rated cabinets to protect components from the weather.

The external fiber jacket and the electronics within the network equipment should be designed to withstand these harsh environments. Look for network switches and media converters with ingress protection (IP) ratings beyond the IP20 characteristic of office-grade equipment. Fanless designs reduce the incursion of dust and moisture, as well as extend the expected lifetime of equipment by eliminating moving parts.

Consider the physical characteristics of the fiber-optic cabling deployed. Stick with glass fiber, rather than plastic, and consider cabling with rugged jacketing that is impervious to any moisture or chemicals in the installation.

If the network is expected to be exposed to spray or wash downs, or is located outdoors, IP67-rated connectors or cable-termination boxes may be required.

Media converters operate at the physical and data-link layers, converting electrical protocols, such as RS-232 or multidrop RS-485, to fiber. Industrial protocols such as Modbus, which operate at the application layer, are transparently handled by media converters.

When converting copper-based signals to fiber-based equivalents, the data is not converted to Ethernet, so a pair of media converters is necessary. In this case, fiber serves as a serial network distance extender-no protocol conversion occurs.

As Ethernet has steadily increased its presence in manufacturing and process-control plants, serial device servers, which network-enable these legacy serial protocols, have become common. A serial device server converts native serial protocols to Ethernet frames, which can then be handled by Ethernet equipment.

Fiber can extending the distance reach of the network to the factory floor where the serial device servers are located, as well as providing immunity to signals passing through electrically noisy industrial environments. Serial device servers are available with either 10/100BASE-TX copper Ethernet ports or 100BASE-FX fiber Ethernet ports.

If using all copper-based serial device servers, a copper-to-fiber media converter can be used to convert the copper Ethernet connection to fiber, achieving the same distance and noise immunity benefits as a fiber-based serial device server. The fiber is protocol agnostic, while providing the benefits of distance extension and noise immunity to the industrial network.

The fiber-optic connection, fiber type, wavelength and speed at each end of a fiber link must match. Fiber-based links also must be fixed speed, due to the light wavelength employed for the different speeds. Fiber types, either multimode or singlemode, also dictate distance limitations, with multimode fiber capable of transmission distances up to two kilometers, and single-mode fiber capable of carrying signals error-free 80 kilometers or more.

Older connector standards such as ST and SC are prevalent in industrial equipment, but at gigabit speeds and beyond small form pluggable (SFP) modules are becoming more common. Select SFP modules with the same care as the other network components and derate operating temperatures to account for the internal heat rise in the switches or media converters in which they are used.
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Title Annotation:Cabling Infrastructure
Author:Felgate, Art
Publication:Communications News
Geographic Code:1USA
Date:Mar 1, 2009
Words:804
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