Using EtherNet/IP in process automation instead of fieldbus
Diagnostic data: Diagnostic data can be a very general term and is defined by the task that is being performed by the technician or operator requiring it. From the device perspective, the device can provide diagnostic data to the automation system, operations personnel, maintenance personnel, reliability personnel, and IT personnel, to name a few.
Some of this diagnostic data can be included in the I/O data structure. For example, diagnostic data for a Coriolis flow meter includes empty pipe detection, sensor drift, sensor error, electronics error, inhomogeneous mixture error, ambient and process temperature errors, and other information. Whatever data are considered critical can be included in the I/O data during configuration.
Devices also need to provide diagnostic data to technicians operating outside the control area and the automation system’s operator interface tools. One example is an electrical and instrumentation technician using device configuration software to reference the voltage delta between the measuring electrodes in an electromagnetic flow meter. With appropriate software, the technician can access the necessary data without interfering with process control operations.
Devices on EtherNet/IP can also be polled by a condition monitoring system to determine if there are any diagnostic messages that need to be sent to maintenance personnel as an alert. An industrial PC equipped with asset management, maintenance, condition monitoring, or HMI/SCADA software can access all the I/O and diagnostic information it needs directly from the devices via the Ethernet interface (see Figure 4). With fieldbus, the same software has to access the information from the process historian or database in a DCS—at considerable extra cost.
Most EtherNet/IP-enabled devices support SNMP. This enables IT technicians to monitor, troubleshoot, and administer network devices using standard network management tools. For example, suppose that IT is monitoring network traffic using an SNMP-enabled tool. The software tool reports that an EtherNet/IP device has exceeded its normalized packet transmission rate, and an e-mail alert is created and sent to a technician. The technician can then use the internal Web server of the device for troubleshooting.
This leverages the investments a company has made in its IT support infrastructure, and minimizes the burden on the process control engineer from having to also be an IT support engineer.
Fieldbus, on the other hand, requires detailed knowledge of the fieldbus architecture and cannot leverage a company’s IT infrastructure; the burden is still placed on the process control engineer to be a network expert. Fieldbus requires specialized training and knowledge, while EtherNet/IP is instantly familiar to process automation and other professionals who have worked with Ethernet.
EtherNet/IP has two main messaging connections: I/O data and explicit connections (see Figure 5). Explicit connections are messages that are not scheduled as with I/O data, but are delivered on demand. While the device is handling I/O data requests, it can simultaneously handle on-demand requests. Figure 5 illustrates the mechanism—UDP/TCP in the TCP/IP suite of Ethernet—to simultaneously deploy the I/O data and messaging data for the CIP library.
These examples demonstrate a few of the various requirements of device diagnostic data and the varied locations to which these data are sent. The ability of Ethernet to allow this simultaneous collection of data from the devices is a key benefit.
Compared to traditional fieldbuses, EtherNet/IP has minimal need to create additional configuration code in the host system. This reduces the footprint of the process configuration on the host. There is no need to have an additional software configuration package for the network or to add additional network interfaces, thus reducing hardware and software costs.
Some of these benefits are derived from the mere use of Ethernet and cannot be wholly attributed to the EtherNet/IP protocol. However, implanting these functions often makes fieldbus installations expensive, cumbersome, difficult to support, and sometimes unappealing. Deploying an Ethernet-based protocol is thus useful in overcoming fieldbus difficulties and objections.
Configuration data: Configuring and documenting a process device in an automation system can be a very time intensive task. EtherNet/IP gives users of these devices several options for configuration and documentation by giving them different access points and letting them use different tools to configure and maintain device configurations.
Ethernet 802.3 provides a large data packet—up to 1,500 bytes—that opens up a large chunk of data in a frame, enabling device vendors to serve up more device attributes than can be communicated over typical fieldbus protocols. This configuration data for a process device is communicated at the I/O data level to the automation system.
This gives the automation system access to the configuration parameters of a process device, allowing the user to determine which, if any, configuration parameters can be accessible to system programmers or operators at the operator workstations. This provides flexibility during start-up and commissioning for personnel to monitor or change parameters while working from within their system configuration programs.
Using EtherNet/IP does not require all users to use the same set of tools. Most devices on Ethernet have a built-in Web server that gives users access to device parameters. This is useful for the IT technician who may not have access to, or training for, process control software or device configuration software tools.
Because the Ethernet/IP protocol uses the standard OSI model, other toolsets become available, and can coexist and function synchronously throughout the architecture.
Maintenance personnel also have at their disposal their own tools, such as asset configuration software and asset management software, for documentation and change management requirements. All this software can reach devices throughout the EtherNet/IP network.
EtherNet/IP provides network access beyond the local area network (LAN) to a wide area network. I/O data can now traverse from one network to the other through standard IT hardware. This gives support personnel access from virtually anywhere in the world, allowing manufacturers and vendors to support their customers remotely.
It also provides segmentation and optimization of networks using tools that IT companies commonly provide to the marketplace. Traditional fieldbus implementations constrain data to their physical network; that data must be accessed through the host or a third-party communication interface.
The volume of data on the network is increasing as users begin to merge their business/financial networks with the plant automation system network. This creates an ever increasing need to segregate, constrain, and secure the traffic so that it does not impact the data throughput of the automation networks. IT suppliers have been providing the hardware and tools to support these needs, and that technology is now employed on industrially hardened Ethernet-based devices.
Some IT vendors are also providing switch diagnostic data as I/O data in the CIP library. This commercially available technology allows the engineer to segregate network traffic inside the common hardware appliances, allowing for even faster propagation of critical data inside the network topology.
There will be some applications where a user may not be able to completely segregate or constrain the data to a virtual LAN or local subnet. The issue now becomes being able to compete for the data packets to be processed in the switches throughout the network. EtherNet/IP has identifiers in the CIP library to allow a switch, configured for QoS, to prioritize these packets over the voice, data, and media packets on the network. Being able to perform these QoS tasks within the network provides the best optimization of the network for the automation network data.
Security is a wide and deep topic and is not addressed in this article, other than to note that EtherNet/IP is able to leverage all of the commercially available security features that are delivered in the IT market today for Ethernet-based networks. There are several publicly available documents for securing converged networks, and the ODVA website has a publication that discusses securing Ethernet networks.
Ethernet has been the dominant commercial network for the past 40 years, and will continue to be in the future. As the convergence of the plant floor to the front office continues its progress, leveraging this future in automation devices will be essential. Process devices will get more intelligent—the past and present demonstrate this. A process device will have a lot of information to share, and will need ever more network capacity and capabilities.
EtherNet/IP will meet these needs by leveraging Ethernet advances, taking advantage of Ethernet’s huge economies of scale. More Ethernet nodes will be connected this—or any other—month than have been connected in the entire history of fieldbus. This economy of scale and the tremendous technological advancements that go along with it is what makes EtherNet/IP more capable than a fieldbus network, now and especially in the future.
Michael Robinson is director of solutions for the Endress+Hauser Sales Center, US. He has 18 years of experience in factory and process automation as a project engineer, product manager, and business development manager. Robinson has a BS in agricultural engineering technology from California Polytechnic State University, San Luis Obispo, Calif.
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