Data cables are the unsung heroes of Industry 4.0 and digitalisation. Without them, everything would come to a halt – literally and physically. However, like typical C parts with low purchasing costs and relatively long delivery times, they lead a rather unspectacular existence. Is this compatible with the key role they play in a smart factory?
In order to meet the highest requirements of machine availability, Coperion trusts in redundant optical ring networks. When it comes to choosing the right fibre-optic cable, the mechanical and system engineers rely on the expertise of HELUKABEL, a leading international manufacturer of cable, wires and cable accessories. The Stuttgart-based company is a global market and technology leader in extrusion and compounding machines as well as bulk material handling systems for the plastic, chemical, food and aluminium industries. Their main products are twin screw extruders for the production of plastics. They achieve a throughput of up to100 tonnes per hour. Coperion's ZSK equidirectional rotating twin screw extruders are the world's most widely used extruders in the technical plastics industry. Compounding takes place in the extruders, where additives are mixed with the plastic to precisely optimise specific properties. Although the extruder is the centrepiece, the overall plant spans – from the upstream plastic polymerisation reactor to the homogeneous compound storage silos – an area containing several multi-story factory buildings. It's not unusual to find cable paths over a kilometre long in the plant, which make them ideal candidates for fibre-optic cables. The longer the data transmission paths, the more a fibre-optic cable’s (FOC) long distance properties come to the forefront. In copper-based data transmission, segment lengths are limited to 100 metres. Beyond that, repeaters are needed to compensate attenuation losses.
Hence, the space taken up by a machine is often the determining factor as to whether copper or fibre-optic cable should be used, particularly if other components such as post-pressing, conveyor or storage equipment will follow. The general rule for data cables in plant and machinery applies if bus communication takes place over long distances, i.e. FOCs must be used to guarantee fast and fault-free data transmission. The fact that potential differences play no role in FOCs is an advantage, especially in plant construction. Nevertheless, it should not be forgotten that Coperion extruders are only part of the overall plant, and that potential differences might still arise between other components. This is not an issue though if data communication is exclusively FOCs.
Fibre-optic cable – the diva of data cables
Compared with copper-based electrical transmission, the outstanding features of fibre-optic cable are its far superior transmission rate over very long distances and the absence of crosstalk between neighbouring fibres. Being optical conductors, glass fibres exhibit resistance to electromagnetic interference, and are electromagnetically compatible (EMC) with electric power cables installed beside them – as long as the FOC does not have a metal sheathing.
The purely glass fibre permits unsurpassed signal transmission, but at a price – the ‘diva’ of data cables must be handled with great care. Depending on the bending radius, high bending losses can develop very quickly in the cable when light power leaks from the core into the cladding with its lower refractive index. In particular, FOCs assembled by less-experienced manufacturers are much more prone to signal attenuation. This is because the connectors or splices made to join the fibres are potential sources of significant insertion and coupling losses.
While simple connectors can be used to quickly adapt copper cable to the respective application, FOC assembly requires expensive equipment, know-how and experience. The fibre splicing and measuring tool alone cost several tens of thousands of euro, which is why many customers prefer to buy professionally-manufactured fibre optics.
HELUKAEL can supply bespoke ‘ready-to-use’ FOCs, together with connection equipment from their extensive HELUCOM CONNECTING SYSTEMS® range. Depending on the application, the cables are connected to a suitable distributor that, without splicing, feeds the fibres in the buffered-fibre cable into individual simplex cables terminated by factory-assembled connectors. Finally, polyamide is used to seal the joint between the cable sheath and distributor to strengthen a typical weak point more effectively than commonly used shrink wrap. The test report shipped with the factory-assembled cable provides information about the joint loss.
Cable expertise directly from the manufacturer
Martin Wurz, electrical design engineer for large extruders at Coperion, is aware of the benefits of partnering with HELUKABEL. "Where could we get better advice than straight from the cable manufacturing experts themselves? Of course, we need to be able to clearly formulate our FOC requirements. Even then, I know HELUKABEL will suggest the optimal configuration and the key account manager will ask R&D their opinion in special cases," he said.
HELUKABEL is well-equipped to deal with these special cases. The HELUCOM CONNECTING SYSTEMS® series of FOC products available in Germany is extensive and includes twelve different types of distributors.
"It's great to know that our product portfolio contains that special something for those out-of-the-ordinary case," says Horst Messerer, HELUKABEL's data, network and bus technology product manager. "Some time ago, Coperion needed an FOC that had to be fed through an outlet with a diameter of just 18 millimetres. We were able to supply a particularly narrow distributor as well as the appropriate cable strain relief."
[Interesting fact: Redundant optical ring
The high reliability of a dual-ring network is due to the physical architecture of two counter-operating rings. Alongside the primary fibre-optic cable ring is a secondary fibre-optic cable ring that transmits data in the opposite direction. During normal operation, data traffic on the reserve ring is idle. When a subscriber or even a section of the FOC fails, data begins to travel in the reserve ring. When data transmits both upstream and downstream of the faulty section, the dual-ring topology becomes a single ring, and overall network performance is maintained.]
Indestructible network topology of the dual ring
The FOCs at Coperion are primarily used as network cables to maximise the reliability of computer communication (visualisation) within the extruder. From the outset, it was known that the control system would cover a large area and that the chosen network topology needed to guarantee high machine availability. Hence, an optical ring with a redundant backup ring was selected for communication between the machine components of the high-capacity extruders.
"High-capacity extruder outages should be avoided at all times, particularly in an industry such as the petrochemical industry, where the downtime costs of an extruder are horrendous. Everything would come to a halt. This is why we opted for a robust optical dual-ring network," explains Wurz. In addition to the architecture-based reliability of the dual-ring, subscribers are connected to the network via managed switches. These switches allow defective subscribers to be directly bypassed so that the reserve ring does not even need to kick into action. This enhances fault tolerance and the dual-ring network is able to cope with more than one outage. Moreover, the resulting infrastructure allows hot-swap servicing and full network component replacement. "Managed switches protect network services in the case of an individual network subscriber outage. The redundant ring is really only intended as a last resort in an extreme situation, or if the FOC ring itself is broken. As far as I know, this has never happened with our high-capacity extruders," Wurz explains further.
The high-capacity extruders can be found all over the world, but particularly in developing countries where operating conditions are extremely harsh. The petrochemical industry, for example, often establishes itself where the feedstock exists. Wurz: "I've never heard of any incident where the data transmission rate of the installed FOC was nearing its limits, which goes to show just how robust the deployed FOCs are."