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Optimizing Ethernet Performance in Manufacturing Plants

Considering environmental risks and selecting hardened cabling, connectivity, switches and hardware are essential to long-term network performance and reliability.

Industrial Ethernet is trending to be the principal infrastructure choice for plant floor networks, just as Ethernet has long been the standard communications protocol in business offices. Both are built on the same standards-based networking platform (Ethernet LAN standard IEEE 802.3). The key advantage of industrial Ethernet is that it allows manufacturers to deploy a single platform to enable interoperability in connecting plant operations to corporate and administrative offices, and the Internet.

This convergence of open, standards-based Ethernet communications between plant and office levels of an enterprise generates advantages for both, including:
•    Ubiquitous access to real-time data to improve plant operations
•    Real-time collaboration, inventory visibility and production planning
•    Shop floor system integration with ERP for scheduling, planning, quality tracking and delivery information
•    Reduced total cost of ownership (TCO) due to faster installation, less costly maintenance and upgrades

Different environments demand different approaches

There’s a huge difference between installing Ethernet in an office environment where cables, hardware and connectivity components are sheltered and protected, and installing them on the manufacturing floor. In industrial sites, network components may be exposed to temperature extremes, UV radiation (sunlight), moisture, oil, chemicals and other contaminants – all of which can degrade the components’ physical integrity and electrical performance, resulting in intermittent outages or even total system shutdown.

{mosimage}Normal plant activities may also pose risk to network components. For example, there may be constant machine movement and vibration, robotic machinery generating power spikes that increase EMI/RFI, forklifts and other mechanized vehicles traversing the work floor. These can damage sensitive electronics − and even the best commercial off-the-shelf (COTS) Ethernet systems are not made to withstand such harsh and hazardous conditions.

The following guidelines are offered to help manufacturers ensure that the plant floor communications infrastructure is built tough enough to withstand these challenges.

Consider the real cost of downtime.  Manufacturers rely on automation, instrumentation and control data communications to relay signals between machinery, devices and control systems that activate events on an exacting and pre-determined schedule, with little or no margin for error.  

Network administrators also require optimal security and manageability 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.  According to one such report, 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).

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 or even catastrophic failure. No matter what the industry, if a switch, connector or cabling system fails, the cost of parts replacement and repair represents only a tiny fraction of the overall costs associated with production downtime.

The indirect costs of Ethernet system failure may include lost productivity, delayed processes, cost of system shut-down and start-up, possible lapses in security and safety, and the loss of service to customers relying on the plant’s output. These can send total downtime costs soaring to hundreds of thousands, even millions of dollars. For example, an automotive assembly plant capable of producing one vehicle per minute would stand to lose profits of about $2000 to $3000 per minute for small car production, and up to $8000/min for SUV and pick-up truck production!

Specify industrial grade components

In specifying Ethernet physical media, data links and network hardware for plant floor installation, it is important to select hardened, industrial-grade components offering rugged construction and durability to provide optimal performance over long service life. High quality industrial-grade Ethernet products should 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.

Other factors to consider include: conformity with the Ethernet LAN.IEEE 802.3 standard; Mean Time Between Failure analysis; mounting options such as DIN rail mounted, rack- or panel-mounted, or devices that bolt securely onto machines; and a small form factor to occupy less space and allow greater density within the limited space of control panels.

Physical media options – cables and connectivity

For the physical media layer, there are a host of industrial-grade products that conform to the Ethernet LAN.IEEE 802.3 standard, while resisting the effects of sunlight, volatile temperatures, moisture and chemical.  Industrial cables will operate effectively in a wider temperature range (-40oC to +85oC) than commercial cables (0oC to +60oC). Selection will depend on each plant’s network configuration and application requirements.  

Industrial Ethernet cables/connectivity include:

•    Heavy-duty, all dielectric, indoor/outdoor-rated optical fiber cabling in single-mode and multimode constructions. Many feature water-blocking agents for added protection in moisture-laden environments.
•    Industrial grade Cat 5e and Cat 6 cables with heavy-duty oil- and UV-resistant jackets. Some Category cables feature a Bonded-Pair inner construction in which the conductor insulation of the pairs is affixed along their longitudinal axis to ensure consistent conductor concentricity and prevent performance-robbing gaps between the conductor pairs during installation and use.
•    Upjacketed and armored cables for extreme environments.
•    Continuous flex cables designed for use with continuous motion machines and automation systems.
•    Low smoke zero halogen (LSZH) cables, waterblocked and burial cables.
•    Cables designed for use with leading industrial automation networking and communications protocols, such as EtherNet/IP (ODVA), Modbus TCP/IP, ProfiNet and Fieldbus HSE.
•    Industrial-grade connectivity components, such as: IP67- or IP20-rated UTP or STP patch cords, connectors, modular jacks and plug kits, adaptors, faceplates and surface mount boxes.
•    Industrial-grade Cat 5e RJ45 and Micro (M12) cordsets and patch cords, including high flex versions.

Switches and hardware options

Similarly, at the information, control and device layers, a wide range of options is available. There are products to support both copper and optical fiber media, and switches capable of data speeds as high as 10 Gigabits per second.  At a minimum, all of these components – switches, connectors, and other hardware – should offer robust construction and resistance to high temperatures, vibration and EMI.

Typical COTS hardware is designed to operate from 0oC to +40oC, while industrial-grade Ethernet hardware operates efficiently from 0oC to +60oC – extendable to -40oC to +85oC. Also, excessive moisture and corrosive chemicals can inflict serious damage to the electronics in commercial switches, whereas ruggedized industrial switches can be securely sealed to prevent ingress of these substances. (Conformal coating is also available for humid/moist applications.)

Industrial Ethernet hardware components include:
 
•    Hardened managed and unmanaged switches which come in a variety of copper/fiber port configurations, port densities, industry approvals and mounting options.
•    Firewalls to secure and isolate a network while still permitting authorized data communications to pass through.  Firewalls with VPN capabilities also allow secure, encrypted communication from a remote location through the Internet.
•    Wireless Access Points, Clients and Bridges in either DIN rail mount or IP67 enclosure-less housings now also support the faster, more secure and noise-immune 802.11n standard.
•    Related accessories, such as hardened power supplies, SFP fiber transceivers and even software that provides network status, alerts and control from the automation network’s software or PLC.

Plan ahead for bandwidth and redundancy 

With an ever-increasing number of Ethernet-cabled devices being added in today’s automation and control networks, it is an industry best practice 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 over time.

One factor often overlooked when it comes to maximizing network uptime and performance is redundancy, which is also considered an industry best practice, especially in mission-critical applications. Two kinds 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.  (See sidebar for more information.)

The last word: Design for end-to-end integration

Another trend gaining traction across the industrial sector is specifying network infrastructure components from a supplier capable of providing end-to-end, field-proven Ethernet solutions tailored specifically to end user applications and environments. As many companies have discovered, taking a “total system” approach can be more cost-effective over the long run in terms of ease of maintenance, troubleshooting and upgrades. And, an integrated system typically results in greater reliability in delivering optimal transmission performance, as well as increased peace of mind for those responsible for optimizing network performance, day in and day out.
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