How should it work: redundant Profibus using fiber optic CI854 and TU847+2 CI840A
Hello, we are using a cable redundant Profibus network on a plant by means of a CI854 at the conroller and a set of TU847 and 2 CI840 in the field for connection of the controller. When using a copper connection breaking one of the connections immediatly makes the CI840's switch to the other connection.
To connect some IO in another area we used fiberoptic to connect the IO. On the controller side we use a Procentec Combrics unit, on the IO side a Procentec
ProfiHub B2FO2 Repeater is used for every Profibus line. When taking out the fiberoptic from the used repeater the CI840's dont notice a broken Profibus line. When taking out the copper connection between the repeater and the CI840 this is, once again, immediatly noticed.
the connections schematic are drawn in the attachment.
For me this give the following questions:
- How do the CI840's determine if the connection is OK;
- Is this normal behaviour;
- How can I correct this.
I hope someone can give me an answer or a hint where to look for an answer.
Update on the question; after testing with the help of Procentec it seems the combination of TU847 with 2 CI840 only switches to the other card if all comminication is stopped. While using fiberoptic with only one fibre broken it is possible for the CI840 to receive communication from the CI854.
The fiber optic module should then stop communication to the CI840 allowing it to change to the other. In the fiber optic modules used this functionality is not profided, therefore redundancy is not working as it should.