SERCOS III – uncompromising precision and efficiency

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 centralized or decentralized automation systems.

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.

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%.

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 guarantees maximum real-time precision.

The jitter on a SERCOS III master is only ± 10 ns. A synchronization accuracy of < 20 ns and a simultaneity of < 100 ns is reached network-wide.

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-real-time channel. Telegram size, cycle time and IP channel bandwidth can be adjusted to make maximum use of the network bandwidth.