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FIELDBUSES & NETWORKS Ethernet becomes slimline & real-time capable

Sep 6, 2019

The proliferation of data transmission standards in factories is coming to an end. OPC-UA and TSN are making Ethernet realtime capable and are finally establishing a consistent standard. The article explores the evolution of the Ethernet, its real-time capabilities and the trends in the Ethernet cables. - Ralf Moebus, Head of Product Management Industrial Data Communication, LAPP

The automation pyramid is crumbling. The individual levels, from the ERP system at the top right down to the field level at the base, were once strictly separate. A level could only communicate with the one directly above or below it. This hierarchy is too outdated for the smart factory, where everything communicates with everything else. For example, an order in the online shop will immediately trigger the corresponding actions in the machine, and the sensors in the machine will report directly to the ERP system if there is a threat of production losses. It’s all about predictive maintenance. The aim is that every customer receives a product that is tailored to them and is made as cheaply as it would be if it were mass produced.

This has consequences for communication networks in factories. When the automation boom began during the 1980s & 1990s and the automation pyramid emerged, the data, which was still sparse at the time, flowed via fieldbus protocols. To cut their products off from competitors, many suppliers created their own fieldbus standard. This continued in the same vein in the 2000s with Ethernet. Once again, suppliers managed to “bend” Ethernet so that there are now a dozen different versions that are all incompatible with one another.

But this may all be about to change. On one hand, users have had enough of grappling with dozens of transmission standards, as it involves accepting a huge outlay for network planning and design. On the other hand, all standards have the same flaw:

Standard Ethernet not being real-time capable. Thus, proprietary real-time expansions that require special network components were developed. This has resulted in the network having “real-time islands”, which restricts the consistent and coexistent transmission of real-time and non-real-time data. When everything exchanges data with everything else in a factory – from the online order page via the ERP and MES systems to the machine and each and every sensor, and then back to the cloud – there needs to be a consistent standard that transmits and processes information reliably and accurately in under a millisecond. This is the only way to make good on the key promises of Industry 4.0 and mass customisation.

Borrowing from technology used in concert halls

The various fieldbus standards are far from extinct, but they are losing so much ground to Ethernet, which has been the dominant force in office communications for decades. As the office and production line need to communicate seamlessly, it was only a matter of time until Ethernet wormed its way into factories. The flaw of insufficient real-time capability is remedied by Time-Sensitive Networking (TSN). This set of standards is based on a proposal by the IEEE802.1 Ethernet working group. TSN is the outcome of the work by the IEEE’s Audio Video Bridging Task Group and was originally designed for the synchronised transmission of audio signals in concert halls.

If automated, there would be many advantages to TSN. All participants in a TSN network are time-synchronised, so they perform the right action at precisely the right time. Its priority mechanisms enable every application to receive their data on time and information can be fast-tracked; bandwidth and time slots are reserved for this. High priority is given to drives, for example, that need to be supplied with the latest data in milliseconds. The compatibility of components from various manufacturers is currently ensured by interoperability testing in several global TSN testbeds.

OPC-UA gives new meaning to data

TSN ensures that data is transferred on time. However, it does not contain information on where it should go and what this data means. There is a second standard to handle this; OPC-UA is an open communication protocol for exchanging data from machine to machine and between machines, the ERP system and the cloud. OPC-UA is now accepted as a de facto standard in communications for the Industry 4.0. It has now become real-time capable with TSN, which enables data networks to be standardised and the flow of information from the base to the top of the automation pyramid to be unimpeded. With this, the pyramid disappears into thin air.

The cables will not change for now as an Ethernet cable does not care which protocol it carries. High quality is what’s important. Perfect shielding, for example, so that the data arrives without disruption. So far, the suppliers of these kinds of cables have been developing them along the lines of “higher, faster, further”. Ethernet cables are now available in Cat.7 version with up to 10 Gbit/s, and even faster versions are about to come into the market.

But is this always necessary? No. Only a few applications – digital image processing being one of them – generate such huge data volumes. It is often the case that “slow” Cat.5 cables can do the same job at 1 Gbit/s.

Slimming is the new black

Downsizing is one trend that LAPP has identified. Fast Ethernet cables have four pairs of conductors. Why not just do without three of the pairs? Just one pair of conductors is all it takes to transmit data, which can still be done at 1Gbit/s. Of course, compatible terminal devices with new, already available PHY chips are required here. These single-pair Ethernet cables will become more important in the future, especially when connecting sensors. The cables are thin, light, robust, fit into tight spaces and can even achieve a range of up to 1200m at 10 Mbit/s. And, of course, they are excellent value for money as they are cheaper to buy and easier to install because technicians only need to connect two cores rather than eight here.

For users who do require the highest transfer rates of 10 Gbit/s, LAPP makes the ETHERLINE® PN CAT.6A fast connect. Inside the cable is a plastic cross separating the four pairs of conductors and features an inner sheath. The fitter no longer needs to remove a foil shield from each of the four pairs of conductors. It saves up to 50 per cent of the time. It prepares the cable for connector assembly in just one step. This saves time and protects the cores when stripping and the inner sheath on the fast connect cable also prevents the core insulation from being cut while removing the shielding.

TSN-capable switches in sight

In the OPC-UA with TSN and single-pair cables one thing is still missing: the TSN-capable active components, such as, switches. Especially, as switches do care which protocols run through them. New real-time capable hardware is needed, and for now, their standards are still being fine-tuned. Many sensors in the smart factory of the future will be connected with single-pair Ethernet cables.

Image Gallery

  • The cables are thin, light, robust, fit into tight spaces and can even achieve a range of up to 1200m at 10 Mbit/s

  • Ralf Moebus

    Head of Product Management Industrial Data Communication


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