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Choosing what's right for you: Ohmmeter vs TDR

Posted: 17 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:T3 Innovation? ohmmeter? TDR? optical-fibre? cable assemblies?

Offering a solution between a basic tester and sophisticated engineering units, field-test instrumentation provides the results needed to verify the basic integrity and performance of copper and optical-fibre cable assemblies.

Cable assemblies, meaning the electrical conductor and associated connectors at one or both ends, are components with a bipolar life. On one side, they're simple copper links and easy to check out for basic continuity; all it takes is an ohmmeter function on a multimeter. On the other side, we expect more and more of these interconnects when handling power and especially when conveying data. After all, who would have predicted years ago that a thin, twisted-pair cable would be handling Mb/s data rates?

Net Chaser Ethernet Speed Certifier

The touchscreen-based Net Chaser Ethernet Speed Certifier from T3 Innovation.

That level of performance is what we routinely get from a properly designed and constructed cable rated for Cat5 or Cat6 standards, for example. Even coaxial cables have their imperatives, with rating to hundreds of MHz and tens of GHz. Yet when a system's performance is not what it should be, we usually don't think about the cable, since it was marked and marketed to fulfil the requisite specifications.

Reality is that counterfeit, substandard, or poorly installed cables are out there, shocking as it may seem. After all, why bother to produce fake ICs when it is so much easier to make or take an inadequate cable and stamp a certification on it? Even better, the substandard assembly will work somewhat, and link problems will usually be blamed on excessive external noise, inadequate noise-margin, timing skew and jitter, marginal line driver/receivers, and many other possibilities.

That's why I like to look through the publications such as Cabling Installation & Maintenance, which target the folks in the field (literally, as well as figuratively). These people are the ones who have to deal with the consequences of designs that worked in prototype and even pilot installations, yet somehow are having issues during or after wider deployment; these problems must be often be worked on under adverse circumstances and in challenging locales. By seeing how field personnel handle these problems, you can often find solutions that work more effectively than you would by using the tools and techniques that design engineers normally have available.

It turns out that specialised instruments are available that quickly and easily test cable assemblies in the field. They're small, lightweight, battery-powered, low cost and easy to use. For example, among their very practical products from T3 Innovation is their Net Chaser Ethernet Speed Certifier that provides gigabit Ethernet speed certification to IEEE 802.3 and cable-test qualification to TIA568 A/B requirements. It checks for faults in the wiring, noise in the network, and provides network discovery and organisation information. (They also have comparable products for CAT-spec'ed cables, coaxial cabling and more.)

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