The impact of Ethernet on AS-Interface
May 2005
Fieldbus & Industrial Networking
Ethernet has become a hot topic in automation. The question is which automation problems will be solved with Ethernet and which will be solved with already existing fieldbus systems.
Will Ethernet replace all existing fieldbus systems like Profibus, DeviceNet, InterBus, CAN and AS-Interface? Will AS-Interface, as the only sensor-actuator-bus system for binary sensors and actuators, disappear - or is AS-Interface the ideal partner system in the sensor actuator level for Ethernet installations?
The problem of realtime data transmission via Ethernet has been widely discussed and has been solved within some limits. Thus automation devices can be connected with Ethernet used as fieldbus. The future will see many fieldbus installations being replaced by Ethernet installations, and both solutions will be used parallel for factory automation. Protocols out of the Internet world such as HTTP and FTP enables standard tools like web browsers to display information. This enables remote maintenance via the Internet. Each device can get its own web server with its own homepage. Different fieldbus systems can be connected to the Ethernet via gateways that act as proxy servers. In that way the respective data of the various fieldbus nodes can be transmitted via Ethernet.
AS-Interface comes from the very lowest level of networking binary sensors and actuators. That aspect has mostly been left out in the discussion of Ethernet in automation. However, it is important because the quantity of binary sensors and actuators makes up about 90% of all automation devices. The development of AS-Interface was based on the requirements of the actuator sensor level.
The intention was that the commissioning of an AS-Interface installation had to be very simple. The easy handling and the quick connection of AS-Interface slaves to the yellow cable using the piercing technology are the big advantages of AS-Interface. A single unshielded two-wire cable is used both for powering the AS-Interface slaves and data transmission. Because of the ability to have AS-Interface modules with only a few inputs and outputs, or even integrated sensors or actuators there is no parallel wiring in machines and plants. Ethernet I/O modules need at least 16 binary I/O to be efficient. Can you imagine a single binary sensor with its own Ethernet interface and homepage?
The big advantage of AS-Interface is the cost efficiency because of rapid cabling, commissioning and also the use of diagnostics in the sensor level. AS-Interface can be connected to Ethernet either via fieldbus, or directly. With the use of Bihl+Wiedemann's AS-Interface/Ethernet Gateway in stainless steel, both Ethernet and AS-Interface can be combined in an optimal way. While control tasks are solved within the Ethernet level, the binary sensors and actuators are communicating via AS-Interface. The use of the gateway's internal web server offers the possibility to display the all AS-Interface data with the help of a standard browser.
AS-Interface is a suitable sub system to network binary sensors and actuators. It does not matter if AS-Interface is a sub system to already existing fieldbus systems or to Ethernet. Users who invest in AS-Interface today can be sure that they have invested in a system fulfilling the requirements of the future. Ethernet and AS-Interface do work together.
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