Fiber-optic technology—it's not just for decorative lighting anymore. In the 1970s, decorative lighting using fiber-optic cable made a statement (dancing pinheads of ever changing colored light) in college dorm rooms, bachelor pads, and the homes of the avant-garde. What might have been creating really neat novelty lighting at that time was not yet setting the industrial world on fire.

Fiber optics has been adapted to industrial use for a number of reasons. In communications, whether in plant networks or process instruments, fiber-optics technology offers advantages over traditional copper wiring or cable. Data can be transmitted digitally and at greatly increased speed. Fiber cable is superior to copper wires because it is immune to corrosion, vibration, and electromagnetic (EMI) and radio frequency interference (RFI). In network applications, it has superior transmission quality and is generally easier to install and maintain.

Mike Shulim, director of engineering for DST Controls, a system integrator located in Benicia, Calif., placed noise immunity at the top of his list of reasons to consider fiber optics in a control network situation. "Additionally, fiber-optic networks have 'no' life," Mr. Shulim commented. "Copper-based systems degrade with age. After 10 to 15 years speed of transmission drops and internally generated noise increases. Fiber-optic systems have an effective life three times that of copper. Definitely a long-term solution."

Additionally, fiber-optic conductors are much smaller, lighter, and more flexible than copper wire. Development of low-cost optical transducers and advancements in optical-fiber manufacturing now makes it cost competitive with conventional wiring. Bandwidth is very high compared to conventional wire cable (two hair-thin strands of optical fiber can transmit the equivalent of 24,000 telephone calls at the same time. It takes two copper wires contained in a much thicker cable to carry just one call. Termination and spicing of fiberoptic cable (especially in the field), once its Achilles' heel, has improved greatly since its appearances in the 1970s, ushering it into prominence in modern digital communication.

Mr. Shulim points out that use of optical fibers in control installations, especially retrofits and system expansions, is cost comparable to running copper conductors. "Users can run fiber-optic cables in the same conduit and trays as existing power cables with no 'noise' concerns and save on installation time and cost."

According to Mr. Shulim, the smaller, flexible cable is generally easier to install, however, technicians must pay closer attention to detail. Overstretching of cable and poor termination can prove disastrous. Quality variations in poorly specified cable can also be a problem. Says Mr. Shulim, "As little as two inches of bad cable can disable a system. In general, fiber optics is less forgiving of installation errors."

Fiber-optic technology has been adapted to control instrumentation applications often for the same reasons that make it a good choice for networking. FiberFlex, a nuclear continuous level detector developed by Ohmart/Vega Corp. (Cincinnati, O.), incorporates a fiber-optic bundle for the device's scintillator.

Nuclear continuous level measurement works by directing a narrow fan of radiation through a vessel to a detector or scintillator. Within a fiber-optic scintillator, radiation creates photons, then measured with electronics and correlated with liquid level. As the process level rises, it shields the detector from the radiation. The more radiation the detector "sees," the lower the process level (discernable to 1% of span); less radiation detected means a higher level.

To avoid "blind spots" and ensure accurate readings, scintillators must conform to the vessel wall opposite the gamma ray source. As the name implies, flexible, lightweight fiber optics allows FiberFlex to be easily installed to measurement lengths of 23 ft.

According to Kevin Carmichael, chief engineer at Ohmart/Vega, "nuclear devices are often the technology of last resort" when it comes to measuring continuous level. Nuclear measurement is used for level values in processes where materials are extremely hot, corrosive, hazardous, or viscous. In short, because of high cost and complexity, it is used when no other technology will work.

Not all fiber-optic materials are created equal. In fact, communications with its "on and off " digital mode can use a different grade of fiber optics than do instruments that must convey a clear image of what the sensor "sees." Used in medical examination equipment such as endoscopes, these materials have been adapted to industrial temperature sensors. In the case of infrared sensors, fiber-optic cable can be used to connect a sensing head that must be mounted separate from the processing electronics. Fiber optics' intrinsic immunity to temperature and electromagnetic interference enhances this type of application.

Marathon FR1 noncontact ratio thermometer developed by Raytek Corp. (Santa Cruz, Calif.) is among practical examples of this technology. The sensor is said provide the accuracy and stability of a two-color ratio-thermometer even in high temperature (in this case, 200 °C) and electrically "noisy" environments. The fiber-optic cable is available in lengths up to 33 ft and can be replaced in the field without need for recalibration. The FR1 is currently available in three models, covering a range of 500 to 2,500 °C. It is intended for harsh operating environments, including metals and glass production.

A common use for this type of fiber-optic instrument is in carbon anode "baking." In the reduction of aluminum, carbon anodes are consumed during the electrolysis process. Efficient manufacture of these anodes, which are often larger than a cubic meter and consumed by the hundreds, is key to aluminum production. Anodes are molded from a slurry of calcified green coke and distilled coal tar. They are then baked in gas/oil-fired pits at temperatures greater than 1,000 °C for several days to develop the best physical and electrical properties. Controlling the baking process requires accurate monitoring of temperature at the top of the baking pit.

Originally handled by Type S thermocouples/protection tubes, pit air temperatures can now be measured more accurately using fiber-optic sensors. Leveraging fiber-optic sensor accuracy, immunity to noise, and ability to mount electronics remotely, many aluminum smelters have embraced fiber-optic sensor technology for this demanding application.

Fiber-optic cable can also be used for level sensing and provide both intrinsic safety and eliminate RFI/EMI concerns. Kinematics & Controls Corp. (Brooksville, Fla.) uses a plastic fiber to send red visible light to a prismatic tip located in the sensor head of a level switch. If the switch is dry, light reflects back to the remotely mounted controller. However when the liquid level reaches and submerges the sensor, light refracts into the media and none is returned. The controller then produces the appropriate output for signaling PLCs or driving relay coils.

Commonly used to monitor levels of flammable liquids, the sensor cables are available in 20-ft lengths for applications up to 100 ft away. Tiny fiber-optic heads, as small as 0.25-in. dia., can fit in tight locations. Use of fiber optics eliminates heat sensitive components at the sensor, allowing the device to sense liquids at temperatures above 300 °F, if required.

Separating electronics from a sensor head via a fiber-optic cable has also been adapted to photoelectric sensor design. Without ability to transmit light to its electronics, photocells would have to integrate sensor and electronics in the package. Size of such packages (even with the degree of electronics' miniaturization now available) can inhibit mounting flexibility and convenience.

According to Charley Strobel, senior tech support engineer, for Keyence Corp. of America (Woodcliff Lake, N.J.), separating the two components offers real advantages. In the case of its FS-V10 Series photoelectric sensors, Keyence provided a small sensor head that could be used in "tight" mechanical locations and allow users to mount electronics in any convenient remote location up to 33 ft away.

Because remote electronics are not "in the way" of the sensor and can be packaged as desired, both electronic and mechanical features can be optimized. "Bigger" electronics can lower response times, provide space for convenient readouts and manual controls, and allow features such as automatic and/or manual calibration. These types of sensors often detect small targets, such as registration and guide marks in web-processes that produce rubber and construction materials (foam insulation, wallboard, etc.).

Damp and corrosive atmospheres can effect traditional copper wiring. Even in standard conduit installations, connections in unsealed or poorly assembled electrical boxes can corrode severely. Additionally, poorly shielded wiring is at the mercy of EFI and RFI. Control engineers faced with altering, expanding, or retrofitting a control system often need to use existing cable trays or pull extra wiring through existing conduit. Addition of new sources of electrical interference, such as motors, generators, standby-power equipment, or factory lighting and their cumulative effect on the control system can be overlooked.

To circumvent these types of problems, Poultry Management Systems Inc. (PMSI, Saranec, Mich.) is using Lucent Technologies' (Avon, Conn.) FiberWire fiber-optic industrial communications system as the backbone of its "chicken house" control package. These control systems are designed to control every aspect of the chicken house environment, including controlling feed, water, light, air circulation, and egg production. The specialized egg production control package has been built to control the flow of eggs coming out of the houses by interconnecting with the environmental control system.

FiberWire links each house's computer to a central computer system that calculates which chicken house is "laying" best on a daily, weekly, or up-to-the-minute basis. This information then helps determine the proper environmental control needed for each house to produce the optimal quantity of eggs. According to Bill Kaufman, PMSI fiber specialist, "FiberWire's construction and resistance to damage, corrosion, and EMI/RFI immunity make it a perfect choice for the system.

"Chicken house environment is dark, damp, and filled with ammonia and methane. Many of these complexes run on 230/460 Volt, three-phase power extending all over the facility creating noise even with shielded communication cables. We had recently retrofitted an older site in Michigan where over $20,000 was spent trying to chase down the noise before turning to a fiber solution," Mr. Kaufman says.

Electrical isolation of fiber-optic cable offered another advantage in this application. PMSI's farms may contain anywhere from 12 to 32 chicken houses, 500 ft long and 60 ft wide. Each house is made of steel and full of wire, a perfect attraction for lightning! "You can imagine what would happen if we would have used copper wiring," says Mr. Kaufman. "Lightning would be conducted all the way through the system taking out everything in its path."

Fiber-optic technology has illuminated many applications since its humble "curiosity" status. According to Mike Shulim of DST Controls, "We have seen its use jump 200% per year for a while now in the controls projects we are doing."

Even with its success in high-tech control and communication systems, those fiber-optic lamps and sculptures are still available for those looking to make an interior decorating statement. If you are looking, I have a few web sites for you!