CIP Safety: Fail-safe communication between nodes

CIP Safety, for functional safety applications on the EtherNet/IP and DeviceNet networks, provides fail-safe communication between nodes, such as safety I/O blocks, safety interlock switches, safety light curtains, and safety PLCs in safety applications up to Safety Integrity Level (SIL) 3.

07/24/2012


Diagram shows how safety data is routed between DeviceNet and EtherNet/IP in CIP Safety applications. Courtesy: ODVACIP Safety, the extension to the Common Industrial Protocol (CIP) for functional safety applications on the EtherNet/IP and DeviceNet networks, provides fail-safe communication between nodes, such as safety I/O blocks, safety interlock switches, safety light curtains and safety PLCs in safety applications up to Safety Integrity Level (SIL) 3, pursuant to IEC 61508 standards and as certified by TÜV Rheinland. CIP Safety devices have been working in the field since 2005, and according to the 2011 World Market for Industry Networking study by IMS Research, CIP Safety is now the largest safety networking protocol, accounting for 30% of all new safety nodes installed. In addition to its use in EtherNet/IP and DeviceNet installations, CIP Safety has been adopted by SERCOS International as the only safety protocol for use on SERCOS III networks. 

Safety application coverage in CIP provides the ability to mix safety devices and standard devices on the same network or wire for seamless integration and increased flexibility. Because the safety application layer extensions do not rely on the integrity of the underlying standard CIP services and data link layers, single channel (nonredundant) hardware can be used for the data link communication interface. This same partitioning of functionality allows standard routers to be used to route safety data. The routing of safety messages is possible, because the end device is responsible for ensuring the integrity of the data. If an error occurs in the transmission of data or in the intermediate router, the end device will detect the failure and take an appropriate action.

This routing capability allows the creation of CIP Safety cells with quick reaction times on one network, such as DeviceNet, to be interconnected with other cells via other networks, such as EtherNet/IP. Only the safety data that is needed is routed to the required cell, which reduces the individual bandwidth requirements. The combination of fast-responding local safety cells and the inter-cell routing of safety data allows users to creates significant safety applications with fast response times. 

Users of CIP Safety on EtherNet/IP benefit from not only the proven benefits of CIP Safety itself, but also the benefits of the CIP and EtherNet/IP. CIP encompasses a comprehensive suite of messages and services for the collection of industrial automation applications—control, safety, energy, synchronization and motion, information and network management—and allows users to integrate these applications with enterprise-level Ethernet networks and the Internet. EtherNet/IP—the adaptation of CIP on standard Ethernet technology (IEEE 802.3 combined with the TCP/IP Suite)—provides users with the network tools to deploy industrial automation applications while enabling Internet and enterprise connectivity, resulting in data anytime and anywhere.

With the application of networked motion growing as an area critical for safety technology, ODVA, the organization that manages the CIP Safety technology, is investigating the expansion of the application coverage of CIP Safety to include safe motion. Using the safety functions defined in IEC 61800-5-2 (Adjustable Speed Electrical Power Drive System – Part 5-2: Safety Requirements – Functional) as a framework, ODVA will be defining the requirements for use of safe motion in systems deploying CIP Safety by considering target use cases and control architectures for safe motion applications; safe motion functions that need to be supported, such as safe torque off and safety limited positions; the required data model; and mapping of a safe motion data model to objects and services needed in CIP Safety to support a safe motion profile. ODVA will also be looking to SERCOS International, which has standardized on CIP Safety and is a recognized leader in the application of networking to motion control applications, for input.

- Katherine Voss is ODVA executive director; edited by Mark T. Hoske, content manager CFE Media, Control Engineering and Plant Engineering, mhoske(at)cfemedia.com.

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