Industrial Ethernet – real time Ethernet under the most adverse conditions

Surely, the definition of Ethernet is well known to all the readers who once occupied themselves with connecting their own computers in a home network. More and more frequently the term Industrial Ethernet is used in connection with industrial systems. We will give you a deeper look into that topic here.

Ethernet Switch

©Tim Reckmann / pixelio.de

Industrial Ethernet – a new generation of fieldbus systems

When talking about Industrial Ethernet, the new generation of fieldbus systems is meant. These fieldbus systems try to make the widely-spread Ethernet standard usable for communication of devices at industrial manufacturing. At the turn of the century hundreds of companies merged together to an association of interest to think about how the well-known Ethernet (IEEE 802.3) can be used as a base for a real-time capable communication protocol in the field of industrial automation. Its purpose is to use only one computer network starting with the supervisory level and ending with the communication of actuators and sensors in industrial manufacturing plants. This trend is therefore called the vertical integration of automation technology.

Data collisions prevent real-time capability

The main problem of common Ethernet is that it is not sufficient for the real-time requirements of today’s automation technology. The term “real-time requirements” means, that information processing systems have to give reliable results within a certain time. The Ethernet standard is not able to fulfill these requirements because data collisions can happen. That means two connected computers try to send their message at the same time. The transmitted messages are overlapping so that the listener is not able to decode them. The Ethernet standard solves this problem using CSMA/CD (Carrier Sense Multiple Access/Collision Detection). In this process all network nodes permanently monitor the communication medium and send a jamming signal when a data collision occurs. The jamming signal is recognized as an error message and a new broadcast begins after a random period of time. Thus, error-free transmission is possible, but communication is not real-time capable anymore due to the occurring waiting time after a data collision.

Nevertheless, to achieve real-time capability several methods are used to prevent data collisions without using such a waiting time. One of these uses tokens that organize which computer has the right to send on the communication medium. By using many different techniques various implementations of real-time capable Ethernet were developed. These are e.g. Ethernet/IP, Profinet or EtherCAT.

Ethernet under most adverse circumstances

Besides the real-time capability Industrial Ethernet systems feature special components. The reason for this is that the main application area of Industrial Ethernet is located in production halls with most adverse circumstances and not in clean offices. Industrial Ethernet components are permanently exposed to vibrations, dust, splashing water and high temperatures. For this reason, connectors, switches and hubs that are adapted to the special environmental conditions are used. Furthermore, these components present a higher interference resistance against electromagnetic waves and ensure a better failure safety. Also the connection of different field devices is performed in a ring structure. That means, that the bus cable is looped from device to device. When a failure happens, the network is still able to work and the operator knows exactly which switch caused the error.

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