- By Bill Wotruba
- October 12, 2007
Industrial plants rely heavily on their automation, instrumentation and control data communications to relay signals between machinery, devices and control systems to activate events on an exacting and pre-determined schedule, with little or no margin for error. Plant managers and control network administrators also require optimal security, manageability and reliability so that network availability attains 99.999 percent uptime or better. Yet analysts report that a large percentage of unplanned downtime in industrial operations is caused by network infrastructure problems.
The cost of network downtime
Physical deterioration or electrical failure in critical data transmission components can lead to unreliable network performance and safety issues, and may lead to loss of critical data, system downtime and even total network failure. According to one industry study, fully 72 percent of network faults can be attributed to failure at the OSI (Open Systems Interconnection) Layer 1 (Physical Media), Layer 2 (Data Link) and/or Layer 3 (Network).
No matter what the industry, if a switch, connector or cable should fail, replacing the part represents only a fraction of the costs associated with production downtime. Depending on the industry, and the size and nature of the business, indirect costs can range from tens of thousands to hundreds of thousands of dollars. That’s why a reliable infrastructure architecture is critical to optimal network performance.
The move to industrial Ethernet
Over the past decade, many leading manufacturers and processors have made the transition from PLC- and PC-based plant floor information systems to an open, integrated Ethernet network built on the same LAN standard (ANSI/TIA/EIA-568B) that has been used in commercial offices for decades. Typically, their goals include increased reliability, consistent high performance, greater ease of maintenance and lower total cost of ownership.
Although both office and plant Ethernets are based on the LAN standard, designing and specifying network components for industrial facilities is far more challenging than designing an office network, where cables are hidden behind walls, in ceilings or under floors, and switches and hardware are sheltered in protected areas.
Manufacturing and processing plants present a very different reality. Many if not most cables, switches and other network components integral to machinery automation and control are located in harsh and potentially hazardous environments – environments that commercial off-the-shelf (COTS) Ethernet systems are not made to withstand. Only environmentally hardened, industrial-grade Ethernet component are tough enough to handle such conditions.
Following are some guidelines and best practices that IT teams, industrial network designers and integrators, should consider in designing and specifying an industrial communications network capable of delivering close to 100 percent uptime.
Evaluating environmental risks
Industrial premises are typically fraught with environmental conditions and mechanical hazards that can have a damaging impact on the physical integrity and electrical performance of installed cabling, hardware and connectivity systems. Examples of environmental risks and their effect on COTS versus industrial-grade components include:
- Temperature Extremes. Extreme cold can make COTS cables stiff and brittle, while elevated temperatures can degrade the plastic used in the cables’ construction and cause an increase in attenuation. Industrial-grade cables typically operate in a wider temperature range (-40oC to +85oC) than commercial cables (0oC to +40oC).
Commercial-grade hardware (switches, etc.) is designed to operate from 0oC to +40oC, while industrial Ethernet hardware can operate efficiently from 0oC to +60oC, extendable to -40oC to +85oC with the use of a conformal coating.
- Chemical Exposure. Oils, solvents, chemicals and cleaning solutions can soak into COTS cables, especially under heat, causing the cable jacket to swell and lose mechanical strength.
On the hardware side, corrosive chemicals can damage the electronics in commercial switches, whereas industrial switches are typically sealed to resist these substances.
- Humidity Levels of up to 99 percent can be accommodated by industrial-grade switches, which can also be sealed to meet IP67 standards. Excess humidity and exposure to moisture have been shown to quickly degrade COTS components.
- UV Radiation Exposure can cause COTS cable jackets to decompose at an accelerated rate, compromising mechanical strength and electrical performance. High quality industrial-grade cables offer superior sunlight/UV resistance, maintaining performance levels even after long-term exposure.
- Physical Hazards. Routine plant floor activity can pose mechanical risks to Category 5e and Category 6 unshielded twisted pair UTP Ethernet cables. For example, machine movement or vibration can pull or stretch cables with excessive force. This can create imbalance between the pairs, degrade electrical performance and increase susceptibility to ambient EMI/RFI. Plant floor vehicles, such as forklifts and moving carts, can accidentally run over cables, causing abrasion, crushing or cut-through. Robotic machinery can generate power spike that damage sensitive electronics.
The best way to optimize the performance and long-term reliability of the plant floor Ethernet is with ruggedly built cabling, connectivity and hardware components designed specifically for use in harsh industrial settings. These products are designed and engineered to provide a lifespan similar to that of other automation system components – typically 10 to 30 years, which is significantly more than COTS products can deliver.
Rugged components to fit each application
Environmentally hardened components for the physical media layer – cabling and connectivity – include both industrial-grade Cat 5e and Cat 6 copper-base cables and heavy-duty, indoor/outdoor optical fiber cables. Upjacketed and armored cables offer extra protection in extreme environments. Continuous flex cables are designed for use with robotics and mechanized machinery, and rugged variable frequency drive (VFD) cables can be used to save energy, while extending the lifespan of motorized equipment.
Connectivity components include industrial-grade cordsets, patch cords and connectors, modular jacks and plug kits, faceplates and surface-mount boxes – all built to last in harsh and demanding environments.
On the hardware side, components include ruggedly built managed and unmanaged switches in a variety of copper/fiber port configurations, port densities, mounting options, and industry certifications. There are firewall appliances to secure and protect the network while still permitting authorized communications to pass through. And there are safe and secure industrial wireless systems and software, hardened power supplies, SFP fiber transceivers, and more.
With so many product choices and so many applications within various industrial sites, it is important to work with an experienced Ethernet system designer or integrator capable of specifying the right products to fit the requirements of each application.
Future-proofing: planning for bandwidth and redundancy
With a growing number of Ethernet-enabled devices being added in today’s automation and control networks, it’s a good idea to allow for sufficient bandwidth to handle current needs, with additional headroom to accommodate future expansion. This is far less costly and labor-intensive than having to upgrade incrementally.
A factor frequently overlooked in maximizing network reliability is redundancy, which is especially important in mission-critical applications. Two aspects of redundancy are key to maintaining uninterrupted signal transmission and maximum uptime.
The first is power source redundancy. Specifying switches that have dual power input capabilities means that if one power source fails, the other immediately takes over.
The second is data path redundancy. The daisy-chain network topologies used by many industrial plants to connect automated machinery and devices have one inherent flaw – if any link between two switches fails, the entire system could potentially go down, as the devices on one network segment can no longer communicate with devices in other segments. The solution is to ensure a built-in redundant data path into the network topology.
Designing for network integration
Another practical way to maximize the value of transitioning to industrial Ethernet is to integrate the plant floor information and communications network with that of the enterprise. As many companies have discovered, taking a converged, total system approach can also be more cost-effective over the long run in terms of network security, troubleshooting and maintenance.
In addition, integrating on a standards-based Ethernet platform provides enterprise-wide visibility and information flow, enabling unprecedented levels of interoperability and collaboration between the business and plant operations. This kind of Ethernet convergence can, for example, allow for:
- More convenient access to real-time data to improve plant operations.
- Shop floor system integration with ERP to improve production planning and scheduling, quality tracking and delivery information.
- Real-time inventory visibility and control.
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