Ethernet Inside the Intelligent Device | Automation.com

Ethernet Inside the Intelligent Device

February 042012

February 2012

By Jessica Forguites, Rockwell Automation

Many people believe the current fascination with Twitter, YouTube and other social media tools stems from a need to feel connected. This push to be interconnected is everywhere, but in manufacturing, it isn’t just a psychological-based need, it’s a critical business imperative.

“Information is crucial for delivering the deep insight engineers need to quickly and efficiently adapt manufacturing operations to changing market demands,” said Craig Resnick, research director, ARC Advisory Group.

To help information flow freely and securely throughout the enterprise, more manufacturers are turning to EtherNet/IP to create a unified network architecture – a step that is arming everyone from operators to executives with the real-time insight they need to make better business decisions. This powerful, versatile technology uses standard Ethernet and IP technology to help simplify communications. EtherNet/IP is ideally suited to help many manufacturers control, configure and collect data from the plant floor to enterprise business systems.

With wide adoption of EtherNet/IP on the plant floor and additional applications now utilizing Ethernet technology – including safety, I/O, motion and drives – IP traffic has increased significantly. Control engineers are working with networks that have increased from hundreds to thousands of nodes on a single network. The growing size and sophistication of these networks makes it important to design proper network segmentation into any plant or machine using EtherNet/IP devices.

Choosing the right topology, switch and network segmentation has become central when employing EtherNet/IP and can add a level of complexity to the overall design of the plant or machines. But with careful planning, the benefits far outweigh the challenges.

Introducing Embedded Switch Technology
One of the ways leading suppliers like Rockwell Automation are helping customers to simplify the design and deployment of EtherNet/IP networks is by designing products with embedded Ethernet switch technology – essentially including the switch in the device itself. Rockwell Automation uses the embedded switch technology standardized by ODVA and the International Electrotechnical Commission (IEC) to help ensure the intelligent device and the technology embedded is interoperable with as many systems and vendor offerings as possible.

So instead of installing just external switches, system designers can install pre-configured, EtherNet/IP embedded switch devices – giving them the freedom to select the most appropriate combination of managed, unmanaged and embedded switches for each application.

Understanding Switch Technology
To best understand the advantages that come with the option of embedded switch technology, one must first understand the basic need for switching technology, and the qualities of managed and unmanaged switches.

Industrial managed switches have played a key role in the success and evolution of EtherNet/IP. They help provide the means to properly segment the network – an important role as IP traffic is increasing significantly as manufacturers add new applications, such as motion and safety, to the network. The intelligence delivered by managed switches allows more sensitive and complex applications to run securely and reliably on EtherNet/IP, while providing enterprises with easy access to manufacturing metrics for business decisions.

Managed switches make intelligent features, such as Quality of Service (QoS), port mirroring, network security and diagnostics available to system designers. While these switches help manage traffic flow throughout the enterprise, all of the bells and whistles may not be necessary for every application.

Unmanaged switches have been an attractive option because of their lower cost and lack of management features to configure. However, unmanaged switches will only perform the basic switching functions on a network, like preventing information packets from colliding. They do not provide any additional features that may be necessary to meet the performance requirements of a machine or application.

Features of Managed Switches
QoS prioritizes network traffic, allowing demanding manufacturing applications, such as I/O and motion control, to take priority on an EtherNet/IP network. Unmanaged switches don’t have QoS and can overload when too much traffic comes their way, introducing delays and jitter (variations in delay) that can disrupt machine operations. On managed switches, QoS prevents this by working much like an emergency vehicle system. When an ambulance or fire engine comes down the highway with lights flashing, other cars on the road know to give the emergency vehicle the right of way. ODVA publishes QoS standards for EtherNet/IP devices to inform the infrastructure of the type of traffic being transmitted (i.e., motion control, time synchronization protocol, safety control or standard control). Without QoS, this information will be ignored and all network traffic will be treated the same by switches and network infrastructure.

Managed switches can provide security by allowing only authorized users or devices access to network resources. Port mirroring is an important feature for diagnostics – providing network “sniffing” tools to capture valuable network data. Network resiliency protocols are used to prevent network outages when cables are broken, switches are powered down, or network loops are accidently created. Managed switches have the intelligence to detect these issues and automatically find new paths to route data so production continues unimpeded.

IEEE 1588 Precision Time Protocol (PTP) is used to synchronize distributed clocks on a network. The transparent clock feature of managed switches will measure and adjust for any network delays, making synchronization more accurate.

These useful features are well-established and now come standard on many managed switches. They’ve proven easy to use with EtherNet/IP because the network uses standard IP protocols, meaning it can work side-by-side with the many commercial protocols for the Internet, e-mail, video and more. This enables users to deploy Ethernet as they have in the past; using standard network products and infrastructure, and leverages the decades of training and experience the world has gained from using Ethernet in business and commercial settings.

Benefits of Embedded Switch Technology
The investment in configuring and managing the functions of a managed switch is well worth it and necessary in many cases, such as managing information flow between the plant floor and enterprise. Embedded switch technology lets machine builders and system designers take advantage of the features of a managed switch without configuration.

Stand-alone managed switches are designed for connectivity to a multitude of devices, but need to be configured for each connection. Embedded switches already know the characteristics of the device connecting because it is embedded in the product itself, so switch management features are already set up and optimized for each device. This is one way embedded switch technology reduces deployment and maintenance time. Increased topology options can add to these time and cost savings.

Increasing Resiliency
Machine or system uptime, which has always been critical, is becoming more so in businesses today where costs and resources are more closely tracked. Ethernet embedded technology enables machine builders to use a device-level ring (DLR) topology that produces a single, fault-tolerant network – thus one that’s more resilient. Here’s how: One device in the ring is designated as an active supervisor. This supervisor sends out beacon frames, or signals that move around the ring. The supervisor will know a break occurs if the beacon frames fail to make it back around to the supervisor who sent the message.
 
If a failure occurs at one of the nodes, the nodes surrounding the failure send back the information to the supervisor. This allows the supervisor to guide a maintenance engineer directly to the node where the fault occurred. Additionally, the network can continue to run as expected, in a linear topology. This recovery occurs in less than 3 milliseconds.

Resilient networks open the door for many more applications to be integrated on EtherNet/IP. Machines that are highly sensitive to any fault or downtime, such as chemical and pharmaceutical production facilities and refineries, or offshore oil rigs, can now use DLR topology to help ensure production continuity and leverage all the benefits of the EtherNet/IP network.

Making Latency Obsolete
Time synchronization is important for any sequence application in automated manufacturing. High-precision motion control, power and energy applications that use alarms and events all require proper timing. With ODVA-certified embedded switch technology, devices come with PTP transparent clock support that facilitates a seamless synchronization of the distributed clocks on the network. Infrastructure devices with transparent clock support will account for any network latency or jitter as clocks are synchronized across a network.

Consider a soda-bottling application. As a bottle moves down the line, it’s filled with soda. Then a robotic device or arm grabs the bottle and positions it for capping, then labeling, etc. Before EtherNet/IP, each device in the soda-packing machine would receive separate messages about task timing. If the timing differed between the robotic arm and the filling device, the arm might grab an empty bottle. Removing the empty bottle from the line takes time, and if it causes the line to be shut down, a lot of money as well.

PTP through an integrated EtherNet/IP network maintains clock synchronization. Time becomes an integral function of the control system and control algorithms. In such a system, all devices have the same notion of time. With PTP, the soda-bottling machine’s robotic arm and filling device stay synchronized.

Higher levels of security, resiliency and reliability on the plant floor are necessary to stay competitive. There have been important new technologies created to serve this purpose over the past decade that are now proven and widely accepted. There will be more to come. Advancements like embedded switch technology make those previous achievements – and all their benefits – easier to use.

Choosing the Best Topology
Traditional fieldbus and data highway networks did not require external switches, allowing machine designers to connect devices directly to one another. With Ethernet networks, such as EtherNet/IP, external switches are required and may limit the system to a star topology.

This becomes problematic for control engineers building a roller coaster, for example. They would want to employ a ring topology because the track is essentially a circle and a fault tolerant network is an application requirement. They can use EtherNet/IP to network the various controllers, HMI and I/O devices running the roller coaster. But without EtherNet/IP embedded switch devices, these engineers would deploy a star topology, meaning every device on the network would have to be connected to the switch itself. This could quickly add up to a costly hardware and cabling system. As any maintenance engineer knows, longer wires mean more complications. If a communication problem arises within a machine, the first step in fixing it is to find the longest wire because that’s often the source of the trouble.

With embedded switch technology, the roller coaster can connect each device directly to the next along a ring or linear topology, dramatically reducing equipment and maintenance costs. Having the switch inside the device also frees up valuable real-estate inside cabinets.

Easier design and deployment are important to all machine builders and system designers, but it is equally important that technology investments continue to make machines and processes perform better.

Leveraging Technology to Best Meet System Requirements
To take full advantage of the capabilities of EtherNet/IP on the plant floor requires careful planning and execution of the network design. Embedded switch technology can help manufacturers and machine builders design, deploy and maintain their networks to easily and cost-effectively maximize their investments and profitability. It makes for a more flexible, simpler network that performs better. Technology advancements like embedded switch technology continue the evolution of the Ethernet, and will further its progress in plant floor applications into the next decade.
 

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