First developed almost two decades ago, many different fieldbus networks still continue to dominate industrial automation and process control. After prolonged prognostications (dubbed the “Fieldbus Wars”), several standards emerged, each focused on different market segments.
Flexibility was achieved through different types of field devices operating with dissimilar networks. Due to the very low quantities of components sold, overall costs remain high for both controls and field devices, and particularly for wiring.
With more than 500 million ports installed worldwide in enterprise networks, Ethernet has become the dominant networking technology and a de facto standard. It delivers wide availability, openness, high performance and cost-effectiveness, and enjoys such wide acceptance because it is easy to understand, deploy, manage and maintain.
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Compared to traditional, non-Ethernet-based industrial solutions, Ethernet technology delivers substantially higher performance. And, because it is based on industry standards, it can run on and be connected to any Ethernet-compliant device from any vendor. However, standard Ethernet has the following disadvantages when it comes to industrial applications:
• It does not seem practical at the lowest level compared with device networks such as CANopen and DeviceNet.
• It is collision-based and not inherently deterministic—and process controls demand real-time operation.
• Its large overhead doesn’t use bandwidth efficiently.
• Universal acceptance of Ethernet tempts users to try to do too many things that could generate security issues.
• Standard telephone-type connectors do not meet the physical demands of industrial equipment.
Despite these drawbacks, industrial Ethernet offers several significant advantages over fieldbus networks:
• Homogenous networking and integration with Internet/intranet.
• Communications over routers and servers where IP-addressing and TCP transport are mandatory.
• Greater bandwidth and larger data packages for communications with intelligent industrial devices.
• Faster real-time communications and synchronization for demanding control applications.
• Ability to connect and address more devices over longer distances and wider areas. This can be crucial in large plant environments.
• Simple to integrate with networks that already exist in the business office environment.
• Online updating of firmware, remote configuration and error handling.
• Huge market for Ethernet products and components makes them inexpensive, widely available and thoroughly tested.
• Ability to use standard access points, routers, switches, hubs, cables and optical fiber.
• A natural fit in the “sensor-to-boardroom” connectivity scenario.
Ethernet technology is rapidly being embraced and promoted by multiple fieldbus standards organizations, including Profibus International (PI), the Open DeviceNet Vendor Association (ODVA), CANopen, Modbus.org, Fieldbus Foundation and others. Connecting with standard Ethernet makes these systems more interoperable.
Bridging the differences
Automation and control protocols differ significantly from standard Ethernet implementations. But major control system manufacturers now incorporate versions of Ethernet networks and higher-level Ethernet-related protocols in their product offerings.
Today, “industrial Ethernet” is being promoted with several different proprietary designs. More than 20 different protocols compete in various segments of this rapidly growing market, each offering adaptations to meet different real-time and cost challenges. Here are some of the leaders:
- Profinet is the open industrial Ethernet standard promoted by Profibus International (PI). This group claims that more than 2 million Profinet devices are currently installed in plant environments; more Profinet than Profibus engineers were certified in 2012.
- EtherCAT (Ethernet for Control Automation Technology) originally developed by Beckhoff, provides real-time performance and supports various topologies with twisted pair and fiber optic media.
- EtherNet/IP (IP for “industrial protocol”) is supported by Rockwell Automation-affiliated organizations, ControlNet International (CI) and Open DeviceNet Vendors Association (ODVA).
- Modbus-TCP allows the widely used Modbus protocol to be carried over standard Ethernet networks on TCP/IP.
- Ethernet Powerlink combines CANopen and offers deterministic real-time operation.
Will there be more than one standard? When fieldbus was introduced two decades ago, the same question was being asked. The parallel promotion of different industrial Ethernet standards increases confusion among end-users. But what was once considered a solution limited to corporate network environments is now a robust technology that can meet the unique needs of industrial environments.
>> Jim Pinto is a technology futurist, international speaker and automation industry commentator. You can email him atjim@jimpinto.comor review his prognostications and predictions on his website:www.jimpinto.com.
