It may seem unbelievable, but fiber optic links and networks have been used for over 20 years. The first telco networks were installed in the late 1970s and data links were already in use by 1980, when there were few personal computers (PCs) and computer networks. These early fiber optic data links were usually based on electrical standards such as RS-232 or 4-20 mA current loops or were proprietary designs.
My first acquaintance with fiber optic data links was with process control systems. Fiber was a perfect solution for transmitting data in a noisy electrical environment or over distances too long for copper wiring. Of course, those same advantages make fiber an ideal choice for industrial data links.
Some of the earliest adopters of fiber optic data links were in factories, power generation plants and other harsh environments. Companies like GE, Westinghouse, Square D, Allen-Bradley and Johnson Controls developed systems using what were then state-of-the-art fiber optic components.
Those components included multimode fiber, which was usually of the 100/140 type with a 100-micron core and a 140-micron cladding and SMA, Biconic or Optimate connectors. Later in the 1980s, the cabling components we know and still use today became the norm: 62.5/125 fiber and ST connectors.
Unlike PC networks, which see major changes in technology every year, these process control systems were designed for long, useful lives. In fact, many of them are still in service, 15 or 20 years later. They still provide their original functions and are living proof of fiber optic systems’ reliability.
But every now and then, something fails. Usually, the failure is not with the equipment itself, but with the cable plant. Connectors get broken or cables get cut. Sometimes the facility is upgrading its cable plant and wants to use the old equipment on a new cable plant with modern components.
Eventually, the user discovers that the equipment they are using requires components that are no longer available in the general fiber optic market. They face a big problem: finding replacements for these older components or replacing obsolete equipment at a very high cost. Obviously, the first call should be to the manufacturer. Unfortunately, rapid electronic development, not to mention the effects of mergers and acquisitions in the last two decades, can stymie this effort.
If the problem is interfacing equipment with incompatible components, such as the SMA connector that was so widely used in process control equipment back then, there may be a simple solution. But asking the cabling installer may not help. Most components today are highly standardized and have been for many years. You can use any connector as long as it’s an ST or SC. Many installers have not been in the business long enough to know about SMA connectors and 100/140 fiber, for instance, or have any idea where to find them.
These two components offer relatively easy solutions to the problem. SMA connectors are still available. Many distributors that offer limited fiber optic lines may not have them, but specialty fiber optic distributors still stock them for both 125- and 140-micron fiber. All SMAs are adhesive-type connectors that may not be familiar to all installers, but are rugged and reliable.
The 100/140 fiber may still be available too, but may not be an issue. It was chosen for LED-based systems in the 1980s to maximize coupling light from the source. Connector manufacturers and installers hated it because it required making and stocking different connectors just for that fiber, as all other fibers were 125-micron diameter.
The 62.5/125 fiber became the standard because virtually all systems that worked on 100/140 fiber could also work on 62.5/125. Today that is even truer, as the lower loss of modern connectors compensates lower LED power coupled by the 62.5/125 fiber. Thus, practically all network electronics can be switched over to the modern 62.5/125 fiber.
But what if you have something totally obsolete and unobtainable? An example is when people at a nuclear power plant called us because they could not find connectors for some 20-year-old controllers. We had had some kits and connectors for that type, which we had used in training long ago, but they had been discarded in a move.
We suggested checking the specialty fiber optic distributors, but struck out there. They tried finding enough patchcords in their facility to reterminate with a modern connector on the cable plant end and the obsolete connector on the equipment end, but too few were found. Finally, we tracked down an engineer at the company who had a drawer full of the obsolete parts and gave them to the user.
Those solutions may work for most users, but sometimes you just have to start over. EC
HAYES is the founder of Fotec, the fiber optic test equipment company and Cable U training. Find him at www.JimHayes.com.