Ethernet down to device-level
Industrial Ethernet-based solutions are now established and gaining popularity for plant networking. Ethernet is preferred by many engineers for automation applications for the simple reason that it allows device manufactures to add previously impossible features. These features make working with Ethernet-based devices easy and convenient while providing plant personnel tools they need to incre...
Industrial Ethernet-based solutions are now established and gaining popularity for plant networking. Ethernet is preferred by many engineers for automation applications for the simple reason that it allows device manufactures to add previously impossible features. These features make working with Ethernet-based devices easy and convenient while providing plant personnel tools they need to increase overall machine uptime and availability:
Integrated web servers simplify diagnostics and configuration,
Fault notifications can be sent via e-mail,
Easy data routing to a PLC and,
Monitor applications on a PC.
With these advantages, it’s no wonder that Ethernet solutions are used increasingly to replace networks like Profibus, DeviceNet and others. However, the farther a user goes down to the lowest networking levels, Ethernet’s capabilities begin to run out, and another solution must come into play.
Match network with function
While Ethernet is well suited for top-level architecture, it is not practical for device networking, particularly where devices have simple functionality such as discrete sensors and actuators. This is important to know since users may not currently be able to purchase many devices with a connection to Ethernet, and must therefore use traditional networking solutions to avoid the problems associated with discrete hard-wired I/O. AS-Interface is particularly well suited for this use for a number of practical reasons:
AS-Interface is a low level solution designed and optimized for efficient transmission of sensor and actuator data. I/O nodes are small and inexpensive, allowing solution providers to develop highly distributed I/O systems, minimizing total cable cost.
AS-Interface provides standard 24 Vdc power to individual devices, which is still not practical via Ethernet. This eliminates the need for supplying power to devices individually.
Configuration and troubleshooting functions of AS-Interface minimizes installation and commissioning time.
By connecting simple devices like sensors and actuators to AS-Interface, the time and engineering effort invested in low level I/O structures is protected. Going from one network (e.g. DeviceNet) to another (e.g. Profibus) is effortless. In addition, the performance of upper level networks is significantly improved, with increases in efficiency of approximately 10x when AS-Interface is used to consolidate I/O.
AS-interface is the only truly independent solution with regard to other networks, since it was not developed by a specific PLC manufacturer.
AS-Interface is the only network where technological modifications are not dictated or dominated by a single company. As a consequence, backplane scanner cards for all major PLCs are available with gateways to virtually any industrial network.
AS-Interface does not compete with or attempt to replace any traditional upper level networks. Instead, it enables users to utilize networks to their full potential, by increasing data transmission efficiency, and addressing installation shortcomings like topology limitations, inflexible I/O distribution, and high cost of physical media including cable, taps and terminators. Complex devices (RFID systems, drives, HMIs, etc.) are still good candidates for these upper level networks.
AS-Interface enables users to network safety devices at up to Category 4, while still transmitting standard, non-safe data over the same network.
Simplify upper-level choice
With AS-Interface at the I/O level, selecting the correct upper-level network for an application becomes much simpler and safer. Since these networks are heavily influenced by system vendors, selecting the PLC for an application effectively selects the network. While most PLC manufacturers support an Ethernet solution, this doesn’t mean they are compatible. The reason is that Ethernet by itself does not fully define a communication procedure.
Users must get used to talking about the specific Ethernet protocol they use. For instance, Modbus/TCP and EtherNet/IP are both Ethernet-based protocols, but incompatible. While both use standard Ethernet frames and employ TCP for data transport, they do not share a common application layer and cannot exchange information. Some manufacturers address this dilemma at the PLC level by designing devices that simultaneously implement several Ethernet protocols. One such device is IDENT Control from Pepperl+Fuchs, an RFID system that supports four different Ethernet protocols: Modbus/TCP, EtherNet/IP, PROFNET and serial stream over TCP/IP.
While selecting a network for complex devices is primarily driven by the PLC platform, using AS-Interface at the I/O level is the right choice in any context. Its flexible gateway approach completely shields the user from any changes that occur at the I/O level, and allows engineered solutions, including control drawings, to be reused as new networks and network protocols become available. AS-Interface combined with Ethernet may very well be the winning combination for the future.
Helge Hornis, Ph.D, is intelligent systems manager, Pepperl+Fuchs. Reach her at firstname.lastname@example.org .
PLC networking platforms
Most PLC manufacturers prefer one traditional device-level network, and an Ethernet protocol. This complicates life for device manufacturers since they have to support multiple platforms. Ethernet-enabled devices are less complicated, since one can operate with multiple protocols. AS-Interface gateways communicate with all these networks and many more:
Rockwell Automation (A-B): DeviceNet; EtherNet/IP
Siemens: Profibus; Profinet
Schneider: ModBus; Modbus/TCP
Mitsubishi: CC-Link; (no preferred Ethernet protocol)
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