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| Electric Drives and Controls - Product Catalog |
| SERCOS III – uncompromising precision and efficiency |
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| Because it delivers excellent performance in practical application, the SERCOS interface has become the leading drive communication technology. High data transfer rates and high precision synchronization make SERCOS III the solution of choice for deployment of decentralized automation systems. |
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Optimal bandwidth utilization
With conventional office Ethernet protocols, user data which is embedded in a defined framework of protocol overhead data is sent as individual packets to each device.
When the amount of information which has to be sent is small (for
example, simple set point data), the overhead accounts for a disproportionate amount of the total data traffic.
Here is a simple example which demonstrates efficient use of Fast
Ethernet bandwidth: if 4 bytes of status data were sent individually to 20 devices, 1,680 bytes would have
to be transferred (the minimum Ethernet packet size is 84 bytes),
but only 80 bytes would be used productively for the application.
This equates to about 5 % of the bandwidth even with the shortest
cycle time. Packet collision would further restrict the useable bandwidth.
In SERCOS III telegrams, all of the device user data up to 1,494
bytes is bundled together plus 44 bytes of overhead data. With
a maximum packet size of 1,538 bytes, the bandwidth which is available for productive data increases to as much as 97 %, and deterministic data traffic is obtained without collisions.
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Keeping jitter to a minimum increases precision
Real-time precision requires accurate signal timing and simultaneous signal execution. SERCOS III cyclic communication ensures accurate signal timing, and unique hardware synchronization combined with minimal jitter ensures maximum real-time precision. The jitter on a SERCOS III master is only ± 10 ns.
Automatic telegram optimization increases efficiency
The number and length of the telegrams on the real-time channel
are automatically adjusted to match the application data volume and number of nodes that are registered.
The cycle time is pre-selected for optimal bandwidth utilization, or it is automatically adjusted to match the data volume on the real-time channel. The portion of the cycle which is not used by real-time telegrams is available for standard IP communication on the non-realtime channel. Telegram size, cycle time and NRT channel bandwidth can be manipulated to make maximum use of network bandwidth.
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