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Upgrade Existing Industrial Networks with Fiber Optics

Fiber optic technology has many benefits for industrial networks including high levels of electrical insulation and isolation, easy installation, survivability in hostile environments and EMI immunity. Upgrading can bring these and more, such as greater security, robustness and signal integrity.

BY MICKAëL MARIE, AVAGO TECHNOLOGIES

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Factory automation, control and management have become crucial to the world’s supply chain. High-volume consumer product and automotive manufacturing, for example, require secure, cost-effective and robust data communications in order to react to problems that, if not corrected quickly, can cause substantial profit loss and customer ill will. 

Designers from many industries turn to fiber optic data links as an alternative to copper media. Fiber optic solutions result in reliable data links that are capable of communicating over distances—ranging from inches to kilometers—and are more immune to noise. Industrial network applications benefiting from fiber optic solutions span in-flight infotainment, locomotive transportation, medical equipment, casinos and wind and solar photovoltaic renewable installations.

Easy to Install Fiber Optics Replace Copper Data Links

Although both copper and fiber are used as a transmission medium, fiber optic solutions offer some clear benefits for the system designer. Industrial Fast Ethernet working over plastic optical fiber (POF) or hard clad silica (HCS), for longer data links, has numerous advantages over copper solutions. While copper-based communication links are susceptible to electromagnetic (EM) fields and emit EM noise, which may interfere with other instrumentation, fiber optic links are immune to EM fields and do not generate any electromagnetic interference (EMI). 

Other advantages of choosing fiber over copper include: low weight, complete galvanic separation between link partners, easy field termination and maintenance, easier installation due to short bending radius, and less susceptibility to performance changes caused by temperature extremes and humidity. Fiber optic solutions are also well suited for noisy, industrial environments that have motors and high-voltage; fast-switching circuits, such as in power conversion; automotive manufacturing; medical systems and renewable energy applications, such as wind and solar photovoltaic farms. Fiber optic technology also offers data security since, for instance, it is almost impossible to tap light wave communications.

As shown in Figure 1, multimode (MM), hard clad silica (HCS) and POF cables provide the highest levels of signal integrity over long distances. Multimode cables are especially suited for control systems in offshore wind turbines (over 3 MW) where they are used as a link between the nacelle and the ground. In these applications link length is more than 200m.

Figure 1
Fast Ethernet communication distances extend to kilometers with fiber technology.

Fiber Media for Higher Reliability and Better Safety

Given that the fiber optic link media is essentially glass or plastic, insulation and isolation characteristics are superior to common copper links in that they are immune from EMI. Fiber optic cables (e.g., 5m POF or 100m HCS as indicated by the red lines in Figure 2), offer advantages in noisy environments compared with copper media. With fiber optic solutions, there is no crosstalk between fiber cables or between fiber and copper cable, which makes data transmission more secure. Fiber cable has high immunity to lightning strikes and helps to eliminate ground loop induced errors. When hazardous conditions exist or the environment is potentially explosive, properly used fiber solutions can help increase safety by lowering the potential damage from lightning strikes and ignition caused by electrical sparking.

Figure 2
Fiber optic links are immune to the EMI generated in industrial manufacturing environments.

In addition to being a more cost-effective solution than copper media, optical fiber—such as single-mode (SM), MM, HCS and POF—can be routed in cable ducts, regardless of nearby power conductors; and it is easier to achieve compliance with electromagnetic compliance (EMC) directives and rules (Figure 3). 

Figure 3
Fiber cable has EMI immunity and communication link distances copper media cannot match. POF= Polymer (plastic) Optical Fiber; SM=Single-Mode fiber; MM=Multi-Mode Fiber; HCS=Hard Clad Silica and CAT5= Category 5 copper cable.

Additionally, in the case of plastic optical fiber, no special tools are needed and installation training is easy. POF cable installations have been used in rugged industrial environments, such as automotive assembly, for over 15 years. POF is also suitable to use for short to moderate link distances, is easy to field install, and helps simplify connections to equipment and exiting networks. Another key design advantage in industrial applications is that maintenance is low.

Fiber cable and optical transceivers/receivers/transmitters all pass rigorous quality standards. Fiber optics technology has been proven in high-capacity telecommunication links where systems may have a product life time exceeding 10 years. In addition, some fiber component suppliers are vertically integrated and manufacture their own laser diodes for transmitters and PIN diodes for receivers. This provides better control over quality and delivery.

Fiber Offers Bandwidth, Weight and EMC Advantages

In-flight infotainment systems are becoming more sophisticated and advanced. While video quality is improving, the use of larger video screens is becoming more widespread. Airplane manufacturers always look for ways to reduce plane weight. Since fiber optic solutions are much lighter and transmit more data than copper, within a single line, fiber optic solutions are a good choice for use in aviation infotainment systems.

Fiber optics technology also shows up in aircraft carriers and cruise liners. In addition, many modern trains also use fiber cable and optical transceivers, receivers and transmitters. Reliable operation of the train’s power source, propulsion system and coach control systems are necessary. However, passenger convenience, information and entertainment systems can also take advantage of the benefits from using fiber optics—high bandwidth over long distance, inherent galvanic isolation, excellent EMC characteristics, and electrostatic discharge (ESD) resistance.

The IEC 61375 Train Communication Network (TCN) standard was created to define communication architecture and protocols for trains. In general, the TCN defines a Wire Train Bus (WTB) and Multifunction Vehicles Bus (MVB). WTB connects the vehicles while MVB connects equipment in a vehicle or group of vehicles. MVB operates over three media types:  RS-485 for short distance, transformer-coupled twisted wire pairs for distances up to 200 meters, and optical glass fiber for distances up to two kilometers. Optical glass fiber is often the preferred media in a locomotive MVB since it has high immunity to electrical noise. Optical fiber connects the controller to devices and subsystems, such as power electronics, motor controllers, brakes and radios. MVB also connects equipment in a coach to control lights, doors, air conditioning and passenger convenience displays for train station and arrival information. Redundancy improves reliability since MVB is backed up by a redundant fiber line and devices transmit on both lines. If one line fails, the other line is available for communication.

Train networks have become more complex, where each station is connected to a central computer for scheduling and event updates. Stations needing to send data back and forth could be a few hundred meters or kilometers away. By using fiber optic cable, more data can be transmitted over longer distance—including video—more reliably than copper cable. In addition, these applications have wires placed side-by-side, running from station to station and from one train compartment to another. When copper wire is used, these adjacent wires can cause interference. Fiber optic cables’ EMI advantages, on the other hand, make them immune from this problem.

In trains powered by the electrical grid, single-phase power is taken from the 3-phase AC power grid line to supply the train’s 2-phase AC power line. This creates an unbalance in the grid that must be compensated for. One of the most common methods of balancing and restoring the power quality of the grid uses Static Var Compensation (SVC) with Thyristor-Switched Capacitors (TSCs) and a Thyristor-Controlled Reactor (TCR). The TSCs and TCR operate and switch on/off at high voltage and current. This creates very high electromagnetic fields that will induce electrical noise into nearby copper lines. Fiber optic cables are the best medium for sending control signals to the devices in SVC systems because of their immunity to electromagnetic fields.

Train signaling can also take advantage of fiber optic technology’s long, reliable data transmission capability in harsh physical environments and in the presence of very high EMI.  

Fiber optic technology has become common in medical imaging equipment such as MRI and X-Ray machines. With all the motors and electromagnetic radiation present, these machines generate high levels of EMI. Their communication and control links must have high EMI immunity for reliable and safe operation. High EMI immunity products and electrical isolation are always necessary components for patient safety, so fiber optic products provide a well-suited solution.

In the entertainment area, casinos have machines connected to the central computer/server for data processing, marketing programs and video surveillance. Security is the most important need for a casino’s communication network. Fiber optics offer a safe and secure network for casino operators, as it’s almost impossible to tap into the signal of the fiber optic cable. 

Finally, the renewable energy market has adopted fiber technology. In some wind farm applications, fiber optics is the only suitable communications technology because of EMI. As wind farms and photovoltaic installations operate in remote areas and even offshore, the wide adoption of fiber technology speaks to its reliability and robustness. Downtime and unscheduled maintenance can significantly impact renewable energy costs and adoption, which must be avoided from the system design level. Fiber links are used inside the wind turbine nacelle, which can be over 100 meters above ground or sea level, as well as for data links between turbines and remote management locations. 

Fiber’s inherent isolation has led to the development of fiber products that need to communicate only over a few inches. A fiber optic short link device is a cost-effective transmitter and receiver that can provide up to 12 kV transient galvanic isolation on a single PCB. Such a device based on 650 nm fiber optic technology is suitable for use in applications such as inverters (i.e. for wind turbines), IGBT/MOSFET drives and medical equipment. Adding a metal shield can help provide even higher reliability.

Fiber Optics Help Prevent Down Time

In terms of speed, reliability and proactive system monitoring, the Avago AFBR-5978Z Industrial Fast Ethernet Transceiver is an example of what can be achieved with the use of optical transceivers. In addition, the device’s temperature range (-25° to 85°C) helps ensure that the transceiver can stand up to the rugged environment of industrial applications.

The AFBR-5978Z transceiver features an enhanced digital diagnostic interface, compliant to the “Digital Diagnostic Monitoring Interface (DMI) for Optical Transceivers” referenced in the multisource agreement (MSA) SFF-8472, in which fiber optics manufacturers propose similar product housing and features for easy replacement of the transceiver. Industrial Fast Ethernet fiber optic networks represent an upgrade path for Fieldbus networks, with a speed of up to 125 Mbaud compared to 2 Mbaud for Interbus, 12 Mbaud for Profibus, and 12 Mbaud and 16 Mbaud for SERCOS. It also provides the open-architecture, multi-protocol interface that permits both standard and proprietary Fieldbuses to interoperate. Upgrading to industrial Fast Ethernet allows machinery on the factory floor to be assigned IP or MAC addresses, which enables high-speed remote diagnostics and machine sequence changes via Internet access.

DMI provides real-time operational information from the transceiver module. Parameters reported include module temperature, power supply voltage level, and receiver input average optical power level. Also with DMI, the user gains the capability of performing component monitoring, fault isolation and failure prediction in their transceiver-based application. In addition, DMI fully incorporates the functionality needed to implement digital alarms and warnings.

At the higher networking level, industrial Ethernet connects engineering and management workstations to industrial Ethernet hubs for data sharing and control across the enterprise. The value proposition is significant. Fiber solutions are available with various data rates and connectors that serve industrial communications and factory automation applications. 

The choice of being able to use discrete or integrated fiber optic component solutions gives the designer the ability to focus on specific design goals. Discrete components give customers the design flexibility to meet their very specific requirements, while the integrated component solution saves design effort, minimizes risk and reduces cost. Best of all, fiber’s inherent technology edge in EMI immunity and isolation characteristics suits the factory environment well.  

Avago Technologies
San Jose, CA.
(800) 235-0313.
[www.avagotech.com].