Ethernet is fast becoming the standard network in control systems for OEMs, systems integrators and end users alike, and one of its key advantages is the flexibility in topology. Meanwhile, cost reduction and increased levels of network availability are driving system designers’ choices in architecture. Recently introduced dual port EtherNet/IP devices further enhance the topology options for deploying Ethernet based networks, offering improved redundancy and reducing downtime. Rockwell Automation explains
A traditional Switched Ethernet network implements a star topology which requires all end node devices to be cabled to a switch (star point). While this approach has proved useful for many solutions, some architectures are better suited to a ‘daisy chain’ linear network topology. Furthermore, the Switch adds cost and cabling to small node count applications.
The advantage of the newly available dual Port EtherNet/IP devices is that they contain a switch that eliminates the need for the star switch and allows the introduction of both Device Linear and Device Level Ring topologies in a simple yet cost effective solution.
The introduction of the Dual Port EtherNet/IP adapter for the FLEX I/O family from Rockwell Automation, for example, allows customers to build more cost effective solutions to simplify network designs while maintaining resilience to faults. The adapters have two EtherNet/IP RJ45 connectors that allow the rack of I/O to be connected in a sequence. This type of serial connection is suitable for connecting devices from one to the next in simple machines, or running the network along a conveyor without the additional cost of switches and extra wiring.
In Star topologies when a cable breaks between the device and the switch, only that device is lost and all other devices can continue to work normally. With managed switches this broken cable can often be detected and reported as an alarm.
In a linear topology network, if a wire breaks or power is turned off on a device, all subsequent devices in the chain will cease to communicate. This linear topology can easily be converted to a ring architecture – improving the device availability in the event of a cable break – simply by connecting the two end devices together.
This ring at device level adds a measure of redundancy that is very effective when a connection fails because a single cable/device failure will not lead to the failure of the other devices in the ring. In fact, a Rockwell Automation Device Level Ring (DLR) network can recover in less than three milliseconds for a 50-node system. During this time, the connection between the Programmable Automation Controller (PAC) and the I/O device is not interrupted. The DRL is able to report the cable/device that has failed to help effective and rapid repair of the system.
The introduction of the Flex I/O Dual Port EtherNet/IP adapter allows users to design mixed Hybrid networks that are a mixture of Linear Star – and even Device Level Ring, where required – using this and other EtherNet/IP devices.
Another advantage concerns the display of system diagnostics via a simple web browser. It has been seen through the increasing use of easy
to access, web-enabled Supervisory Control and Data Acquisition (SCADA) systems that reduced downtime and decreased time between fault identification and remedial action is helped by web-based accessed dashboards and alarm systems.
As with all automation systems, the greatest improvements will be made by assessing the system as a whole. Changing one core component, however, especially as part of a plant wide improvement plan, has the potential to make an important difference at the time it matters most – when a fault occurs.
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