Detailed view of a potted splitter body. This is equipped with a compatible screw connection for installation in splice boxes. The system can also be reused for new installations.

© Helukabel, Coperion

While copper cables can be quickly and easily adapted to the respective application using connectors, the assembly of fiber optic cables requires expensive equipment, know-how and experience. Acquisition costs of several tens of thousands of euros for the tool for splicing and measuring alone speak in favor of using pre-assembled fiber optic cables. Depending on the application, the cables are connected to a suitable splitter, for example, which guides the fibers from the loose tube cable without splices into individual simplex cables, which in turn are terminated with pre-assembled connectors. Finally - at least in the case of Helukabel's 'ready-to-use' solutions - the transition from the cable sheath to the split body is encapsulated with polyamide, which makes the typical cable weak point significantly more robust than an otherwise frequently used shrink sleeve.

At Coperion, the fibre optic cables are mainly used as network cables for fail-safe computer communication (visualization) within the extruders. It was clear from the outset that the control system would have to extend over long distances and that the network topology would have to ensure particularly high machine availability. The machine components of the large extruders therefore communicate in a redundantly designed optical ring.

A station failure is bridged via the redundant ring. As there are no switches between the stations and the network in this example to bridge the failure directly, the ring can do this itself using a reserve ring.

© Picture: Helukabel, source: U. Ring, Handbuch Netzwerktechnologien

Martin Wurz, Electrical Designer Large Extruders at Coperion, explains: "We want to prevent all failure scenarios of a large extruder at all costs. Especially in a process industry such as the petrochemical industry, the downtime of an extruder would result in immense downtime costs. That's why we rely on the robustness of an optical double ring network." A double-ring network achieves its high reliability through its physical architecture as a counter-rotating double ring. In addition to the primary fiber optic ring, there is a secondary fiber optic ring on which the data traffic runs in the opposite direction. During normal operation, the data traffic rests on the reserve ring. If a subscriber or even a section of the fiber optic cable fails, the data traffic also runs via the reserve ring. The data is sent back before and after the failed section. The double ring structure then becomes a single ring, but the network as a whole is not interrupted.

In addition to the architecture-related fail-safety of the double ring, the network participants at Coperion are connected to the network via managed switches. This means that if a participant fails, it can be bridged directly with the switch, so that in this case there is no need to fall back on the redundant reserve ring. This increases fault tolerance and the double-ring network can cope with more than one failure. It also provides an infrastructure in which all network components can be maintained and replaced during operation.

Wurz explains further: "As the managed switches already regulate the network security in the event of the failure of individual network participants, the redundant ring is really intended as a final lifeline in extreme cases. Or in the event that the fiber optic cable of the ring itself is broken. However, I have never heard of this happening with any of our large extruders." The latter are located in all parts of the world, often in emerging countries with extremely harsh industrial conditions. The petrochemical industry, for example, often locates itself directly where the relevant deposits are found. Wurz: "However, I have never heard of a single alarm where the transmission level of an installed fiber optic cable is in a critical range. That speaks volumes for the robustness of the fiber optic cables used.

Author:
Jürgen Berger is Head of the Data, Network & Bus Technology department at Helukabel.