Keywords:IT, Control, Networks, Convergence, CIP, ODVA, Ethernet, IP, TIA, IEC.
Panduit recently briefed ARC Advisory Group on the company's physical infrastructure solutions. These are designed to help bridge the gap between the IT and control domains in manufacturing plants and other industrial facilities. The briefing covered best practices for operating companies to use when implementing their networking cabling infrastructures and how each network layer can affect plant uptime and long-term reliability. According to Panduit, companies often overlook the need for proper planning in the network topology, which facilitates higher performance, effective troubleshooting for faster recovery from a downtime event, and provides a foundation for future network expansion.
Initially, networking for industrial automation applications largely involved simple point-to-point connections between devices and controllers. As the number of connections network layers increased, more sophisticated network architectures became necessary.
Point-to-point connections are still commonly used between devices and switches or between switches. However, with the convergence of the IT and control domains, point-to-point connections can negatively impact network predictability and reliability, which in turn can impact productivity and profitability. For this reason, Panduit stresses the importance of a reliable, well-proven, structured physical infrastructure architecture built on standards from both the enterprise IT and industrial control domains to speed deployment of validated, high-performance network architectures.
Structured cabling is a planned cabling system that systematically lays out the wiring and wire management necessary for voice, data, and video communications. Structured cabling starts at the demarcation point where outside communications connects to the on-premises wiring. It then works its way to the control room and telecommunications equipment as part of the vertical or riser cabling that connects equipment rooms (usually between different floors), as well as the horizontal wiring that connects equipment rooms to individual outlets or work areas (usually on the same floor). It is also found on the plant floor, connecting production and other equipment to outlets of the horizontal cabling system.
Structured cabling is a well-understood, standards-based approach. It is applicable across all types of facilities, including office buildings, data centers, factories, and heavy process plants. With structured cabling, horizontal cables use solid conductors, which offer the best attenuation performance over longer lengths. Horizontal cables are terminated with easy-to-install, reliable, high-performance jacks, typically mounted in patch panels, outlets, etc. Flexible patch cords at the ends of the channel enable link testing to be performed prior to finalizing the configuration.
This provides the foundation for delivering plantwide integration, high performance, reliability, and flexibility for future network growth.
Fundamental Concepts of Networked Communications
Industrial network communications have evolved from proprietary bus protocols to open, standards-based communications types such as Ethernet. According to Panduit, within the broad umbrella of Ethernet communications available for industrial automation applications, choosing Ethernet built on standard unmodified IP (Internet Protocol) Ethernet communications offers many advantages. These include a standard physical layer, simplified convergence, and future compatibility.
Ethernet/IP, a subset of the Common Industrial Protocol (CIP) administered by ODVA, is built on unmodified IP standards. The ODVA physical layer specification, which defines layer 1 cabling and connectivity, calls for cabling types that address industrial environmental risks as described in TIA and IEC standards. For harsh industrial environments as characterized by "MICE" (Mechanical/Ingress/Chemical-Corrosion/Electromagnetic), TIA and IEC recommend industrial-grade cabling, rather than commercial-grade, Cat 5/6 cabling.
Considerations for Point-to-Point Cabling
Where point-to-point cabling approaches might be appropriate, it's important to pay careful attention to signal quality, attenuation, and agility.
With point-to-point cabling, the connection between the control panel and the device is made by terminating the cable at the control panel end with a plug located on each piece of equipment in the panel. The cable is then typically pulled or routed between the end points and one end terminated in the control panel. The other end of the cable is terminated at the machine end and plugged in to provide a data connection.
Current practices favor stranded-wire cabling for point-to-point connections. While this is usually advantageous to accommodate areas where tight bends are required, the maximum length for stranded cable will be shorter than for solid cable, since stranded cabling has higher attenuation per unit length than solid cable. To accommodate subsequent reconfigurations with point-to-point cabling, the cable must be manufactured with excess slack, rather than cut to exact length, to enable the new terminations to be added. This is because re-termination would involve removing a short length of cable, causing the overall assembly to be too short and requiring an entirely new cable. (Splicing can be a recipe for disaster, potentially introducing ingress noise at the splice point as well as the potential for line loss and signal degradation).
Best Practices for Cabling
Using patch cords and patch panels is the well proven, standard IT alternative to point-to-point cable assemblies. Instead of field-terminating plugs, jacks are installed at each end of a permanent link run between locations. Patch cords that are pre-terminated and tested in the factory are then plugged into these jacks, helping assure compliant performance and reducing troubleshooting requirements. ANSI/TIA-568-C structured cabling standards recommend use of solid conductor cabling properly terminated at each end with a jack connector, rather than a plug, to form the horizontal cabling, or permanent link, portion of the physical channel.
This structured approach requires more upfront planning and coordination to consider the locations of the patch panels, as well as the number and length of pre-terminated patch cables required for the control panel and machine dimensions. Patch cables are available with both industrial M12 connectors and commercial type RJ45 Ethernet connectors, or to match the environmental MICE rating considerations. For applications that require pulling patch cables through conduit, field-installable connectors can be employed just as you would for point-to-point cabling. This upfront planning and coordination brings structure and predictability, simplifying subsequent troubleshooting, expansion, and maintenance activities.
Benefits of a Structured Cabling Approach
According to Panduit, moving from a point-to-point method of cabling to a structured approach provides numerous benefits. It allows tested connections to remain in place and, with variable length and tested patch cords, enables rapid configuration and subsequent re-configuration, if needed. If the patch cord should be damaged (not unheard of in industrial environments), just the cord, rather than the entire cabling channel, would need to be replaced. Panduit believes that while it requires adequate pre-planning, the structured approach allows for higher performance, greater reliability, and -- ultimately -- higher productivity on the plant floor.
Clearly, networked communications are becoming ever more important in industrial automation applications, enabling the convergence of distributed systems.
Over time, many enterprise IT departments have found that structured cabling to networked communications provides a system that is easier to test and troubleshoot, make additions to and modify, and more reliable over the long term. This has been proven through Building Industry Consulting Service International (BISCI) and Telecommunications Industry Association (TIA) standards and methodologies.
Panduit describes itself as a world-class developer and provider of physical infrastructure solutions that improve industrial automation system reliability, security, and safety while reducing deployment and operating costs. Working with industry leaders, the company helps bridge the gap between IT terminology and control theory to assist in the convergence of distributed systems that provide a structured approach for architects, designers, controls engineers, system integrators and IT professionals. According to the company, this enables the consistent deployment of sustainable infrastructures. Panduit Industrial Automation solutions leverage its Unified Physical Infrastructure (UPI) approach, which helps customers integrate their core business systems for a smarter, unified business foundation.
With so many manufacturing and other industrial organizations today struggling with a shortage of internal resources, particularly for non-core activities such as network implementation and support, ARC believes that it makes sense for those organizations to investigate solutions from dedicated networking suppliers such as Panduit who know this space inside and out as potential networking partners.
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