I’m convinced that there’s value to us using fiberoptic cabling for some of our long and noisy control signal connections between machine trains. But we have a degree of regular, routine reconfiguration of the machines that means making, breaking and changing control and signal wiring configurations. It looks like it’s too hard, or is too much of an art, to dependably make these fiberoptic cable and connector connections ourselves, and we’d be forced to go outside for it each time. Advice please.
ANSWERS
Push-Pull Connection
That was very true in the past. Fiberoptic connections, while very fast and reliable, were difficult and time-consuming to complete in the field. Available connectors were fragile and often not compatible with harsh industrial environments. In the past few years, there have been several innovations in the use of fiberoptics on the plant floor. The development of new fiberoptic materials and connection systems has made fiberoptics suitable for industrial applications.
One example is the push-pull connection system featuring the miniature SC duplex connector, known as the SCRJ. While this system was designed originally for the European auto industry, it is useful in a wide variety of machine-building applications. The innovative push-pull connection technology makes it very easy to connect or disconnect with just one hand.
The SCRJ is compatible with most fiber types. The easiest to use is polymer optical fiber (POF), which has the same transmission properties as Cat. 5e Ethernet cable, 100 Mbps over 100 m. A person with no experience with fiberoptics quickly can learn how to make fast, reliable fiberoptic connections using the push-pull connection technology. The push-pull connector provides an IP67 connection that is fully sealed to prevent the ingress of liquids, dust and dirt.
August's Problem
This probably is more complicated than I think, but what are the critical hardware, firmware and/or software differences between a safety PLC and a “regular” PLC? Can I really use just one for both functions now?
Send us your comments, suggestions or solutions for this problem. We’ll include it in the August ’09 issue and post it on www.ControlDesign.com. Send visuals if you’d like—a sketch is fine. Email us at [email protected]. Please include your company, location and title in the response.
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There are other fiber types available for faster transmission speeds and longer distances up to several kilometers. While a little more involved, users can use field termination kits to quickly complete reliable fiberoptic connections. Fiberoptic connections offer advantages such as fast transmission speeds, long distances and EMI immunity. As for breaking down and changing control and signal wiring configurations, the connectors are very robust and are specifically designed for such applications.
Chuck Dawson,
product marketing lead specialist,
Phoenix Contact, www.phoenixcon.com
Media Conversion
It is true that the use of fiberoptic cabling is a great solution for long network cable runs or in situations where there is a large degree of electromechanical or magnetic noise.
Let’s consider the need to make, break or change wiring, or perform signal wire modifications at the machine level. Fiberoptic cables and their respective connectors are not designed for repeated coupling, nor are they easy and cost-effective to terminate. A very simple and quick option would be the use of a media converter. A media converter is an active device that converts Ethernet signals from one format to another. One standard configuration of media converter is fiberoptic to RJ45 copper.
Placing a media converter in close proximity to each machine will enable the use of fiberoptic cables over long distances or in areas of high noise and would provide the ability to use copper connections via a standard network cable such as a Cat. 5 cable with RJ45 connectors. Standard copper (Cat. 5) patch cables could be used to make the direct connections with the machine via the media converter. This would provide flexibility in making connections and multiple reconnections.
For added flexibility, many manufacturers produce small network switches that have fiberoptic ports and a number of RJ45 Ethernet ports. There are versions available with two fiberoptic ports and six standard RJ45 connections. One of these switch devices can be used in place of a media converter, allowing additional network or signal connections while using the original fiberoptic cable. Using this solution, the fiberoptic line would remain unchanged and local connections, modifications or maintenance could be performed with standard Cat. 5 cables.
Bruce Hofmann, director of marketing,
Weidmüller North America, www.weidmuller.com
Make It Longer
In the reader’s continuously reconfigured application that requires ongoing changes in cable lengths, problems could be avoided by deliberately making a fiberoptic cable “too long.” The reader could then carefully store the excess cable loop in the side of an electrical cabinet. Users of fiberoptic cable should take care to ensure that the cable’s bend radius is never smaller than the minimum allowed by the vendor.
The benefits of fiberoptic cabling for some applications are partially economic and partially technical in nature. If the application has highly distributed equipment, the cost of fiberoptic cabling (glass fiber) can drastically undercut the cost for comparable copper wire.
As the reader is probably well aware, copper in other forms of cabling can degrade due to weather conditions and is more susceptible to electromagnetic and electric field interference. Light transmission does not suffer from those issues. In the case of fiberoptic transmission, the light source must continue to modulate at the correct brightness for the receiver to work properly. This is the biggest consideration when using fiberoptic technologies.
Kurt Wadowick, I/O systems product specialist,
Beckhoff Automation, www.beckhoff.com
