Testing the physical infrastructure

17 August 2021

The role of Ethernet continues to expand, supporting the high speed transfer of data. Mark Mullins describes some simple cable testing options. 

When it comes to deploying Ethernet network infrastructure to support data transmission, certification testing is the key to ensuring that the supporting cable plant is installed correctly, complies with industry standards, and will support applications.

Certification testing measures key performance parameters and compares them to industry standards set by TIA or ISO/IEC, with results indicating compliance with the standard and/or a specific category or class of cable. This, in turn indicates which industrial Ethernet applications the cable plant can support – a critical piece of information needed to leverage Industrial Internet of Things (lloT) technologies.

It is recommended that certification testing be a requirement on any cabling project specification. Indeed, it is often required for obtaining vendor warranty on the cabling system. 

Unfortunately, network problems can arise after successful installation. Some of the most common causes include accidental damage to cables and connectors from workers and machinery; electromagnetic interference; miswiring or improper terminations; or dirty fibre optic connector endfaces caused by exposure to dust. There are some inexpensive tools that can help Operations Technology (OT) staff identify and locate problems.

Copper troubleshooting
A non-functioning copper link is often a result of a lack of continuity caused by a cut or break in the cable or a bad termination process. Testing for continuity is accomplished with wiremap testing that looks for opens, shorts, reversed pairs, cross pairs, and split pairs.

While the certification tester used for initial testing will conduct wiremap testing, few OT departments own these complex, expensive tools. Fortunately, verification testing using a simple, low-cost wiremap tool is an ideal solution.

Identifying the actual location of a fault along a length of copper cable can be easily achieved with an inexpensive tone and probe, which works by injecting a high harmonic signal onto a conductor that generates an audible noise at the fault location. Somewhat more sophisticated verification tools include a Time Domain Reflectometer (TDR), which indicates the distance to a cabling fault, greatly reducing troubleshooting time. 

While verification is the first line of defence, if it is found that continuity is not the problem, qualification testing may be needed. A qualification tester includes alI of the verification functionality but is more sophisticated and can qualify cabling bandwidth on live Ethernet networks to determine if the cable supports the intended application. A good qualification tester will indicate if the problem is related to noise issues.

Fibre troubleshooting
The most common cause of fibre optic failures is contamination caused by dust or dirt on the endface of a fibre connector. Some inexpensive tools exist for dealing with typical problems. One tool to have on hand is a basic fibre inspection camera that can reveal a dirty fibre end face at a connection point. If dirt is visible the connector end face can be cleaned using wipes and solvents. 

There is also a chance that the fibre is bent or broken somewhere along the link. A simple visual fault locator (VFL) will illuminate a fibre with a visible laser that will leak out where the fibre is broken or bent. 

It may make sense to invest in a more sophisticated fault locator that bridges the gap between a VFL and an expensive OpticaI Time Domain Reflectometer (OTDR), which is a more complex troubleshooting tool that requires more skill to operate. There are fault locators available that locally display the location of events such as severe bends, high­loss splices, breaks, and dirty connectors that can impact transmission.

The key to a worry-free cable plant starts with quality components and installation by a qualified installer, followed by certification testing. But if something goes wrong down the road, troubleshooting the problem can be your first line of defence. It may allow OT teams to fix the problem or at least cut down on the cost of repairs by eliminating the need to pay for diagnosis.

Mark Mullins is global communications manager at Fluke Networks.

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