Ethernet Powerlink – The Ethernet Real Time Protocol as a Field Bus System for Automation
Ethernet bus systems are used in wire connected office networks everywhere. In the past, the characteristics of collision-afflicted data traffic have disrupted automation applications, so that a strictly deterministic transfer has not been possible. To take care of the various and special data transfer requirements, a lot of different fieldbus networks have been used in automation solutions.
With the development and opening of the Ethernet Powerlink protocol, completely new possibilities are available to allow the use of a standardised non-interrupted network system from the company floor network level up to the fieldbus system. On the one hand, a fieldbus Ethernet connection made by a Managing Node (MN) with Controlled Nodes (CN) makes a collision free real-time network function possible. On the other hand, using the asynchronous part of the protocol, the upper level network structure can be connected to the real-time components.
The physical base of the Ethernet Powerlink protocol is the normal Fast Ethernet 100Base-TX network. The difference of the Powerlink protocol is the combination of asynchronous and isochronous parts in a cycle. |
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| In the case of real-time requirements in this real-time part of the network, only Ethernet Powerlink units can be connected. In this way, one Managing Node is required to control the Controlled Nodes by the strictly deterministic synchronous protocol part. The cycle time is dependent on the number of the connected Controlled Nodes. With the smallest configuration (1 x MN and 1 x CN), a minimal cycle time of 200 µs can be achieved. The accuracy of the cycles (Jitter) will generally be 1 µs or lower. |
By using the asynchronous protocol part, the Controlled Nodes can be IP addressed from each browser through the connection of the Managing Node with the standard Ethernet. This produces a continuous network structure. Direct access to the individual network units, for example via internet, will be available up to the Ethernet Powerlink network. Should no real-time functionality be necessary, the Ethernet Powerlink units can be used in standard Ethernet network too. The topology of the Ethernet Powerlink network is very flexible. Depending on the technical construction of the Controlled Nodes, standard Ethernet Hubs or Switches, a star or daisy-chain topology or a mixture of both will be possible. |
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| The Ethernet Powerlink protocol is open, which makes it possible for all interested manufacturers or users to utilize it. The "Ethernet Powerlink Standardization Group", as an open non-profit organisation, offers the basics. Standards and agreements worked out by this organisation guarantee the functional cooperation in an Ethernet Powerlink network consisting of devices from different manufacturers. SHF Communication Technologies AG is a member of this organisation. For current information please have a look at the internet presentation www.ethernet-powerlink.org. |
