The line redundant interfaces of CI854A, RLM01, etc. can be connected to the ring by connecting each line to a separate optical link module. It is also possible to configure the master and slave redundancy as an option. The figure shows both CI854A and CI840 in a redundant configuration. If they are used in a non redundant configuration it has to be taken into account, that the disturbance of one optical link module can cause a failure of the connected module. The optical ring in combination with the line redundancy can only be set up by using the optical link module “OZD Profi 12M” from Hirschmann. Other optical link modules will get collisions of data frames that results in a complete disturbed communication on the PROFIBUS.
Using a redundant PROFIBUS system makes it possible to considerably increase the availability and thus the reliability in comparison with a single system. One particular advantage is scalable redundancy that begins with a redundant PROFIBUS transmission link, continues with a redundant master and ends with a redundant PROFIBUS slave.
The AC 800M controller is linked to the PROFIBUS master module CI854A. When a CI854A module fails or bus communication is interrupted, the redundancy partner is automatically activated. A CI854A pair balances the data cyclically via the CEX bus.
Line redundancy requires a redundant transmission medium and a redundant bus connection on the PROFIBUS master. The two transmission media are electrical cables in the simplest case, or fibre optical cables for higher requirements. For optimal usage of line redundancy, master/slaves/links with two bus terminals are required. The master, slave or link detects the failure of a line and continues communication over the intact redundant line. The requirements for line redundancy involve immunity to open circuit, short circuit and error adaptation in respect of cables, connectors, repeaters, media converters and links. If the PROFIBUS slave has not been implemented a redundant PROFIBUS interface, and if, however, an analysis of the system availability shows the necessity of redundant PROFIBUS cabling, it is recommended to use a Redundancy Link Module RLM 01.
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