A universal network for automation

Mark Freeman of Siemens Automation and Drives discusses how the latest developments in Profinet have made it a universal communications network for all automation tasks.

Today's machine designers are coming under increasing pressure to develop machines which meet seemingly contradictory criteria.

For example, the machines have to perform more complex functions, yet must employ a simple architecture.

They must offer higher performance, yet last longer.

And they must be more sophisticated to fulfil a wider range of operations, yet developed and delivered in a far shorter timescale.

Of course the machinery users are under significant pressure too.

With profits being squeezed, productivity is all-important, bringing to the fore the need for improved diagnostics and the need to integrate the machinery more tightly into the wider enterprise systems.

Both OEMs and machinery users are beginning to ask, therefore, whether industrial Ethernet can provide a universal networking backbone for control and communications.

With Ethernet already a standard for communications around the higher level enterprise systems, the ability to link directly into the heart of a machine's control systems dramatically simplifies the collection and analysis of diagnostic information to facilitate condition-based monitoring.

It also allows the production to be tied more closely into supply chain logistics and customer demand.

For OEMs, the ability to standardise on industrial Ethernet for control and communications around the machine offers the potential to dramatically simplify the overall design.

With all the communications taking place over a single bus, the number of interfaces is minimised, programming overhead is reduced and significant cost savings can be realised.

Many have argued that we would never see the panacea of a single communication system suitable for all automation tasks.

And it did seem for a while as if even industrial Ethernet might never be up the more demanding aspects of machinery automation, such as critical real-time operation and complex motion control.

But the ongoing development of Profinet has provided an open and innovative industrial Ethernet standard that fulfils all automation requirements.

Profinet was the first industrial Ethernet standard to deliver features such as industrial-strength installation technology, connection of distributed field devices, simple network administration and diagnosis, and high machine and plant availability.

Together with the availability of industrial-strength Ethernet connectors and cables, Profinet offers the potential to provide a single bus for all communications requirements.

And being built on international open standards, Profinet offers a high degree of investment security.

Most recently, and crucially for OEMs, Profinet has gained real-time capability and determinism, making it an ideal networking technology for even demanding isochronous motion control applications.

For real-time tasks, Profinet user data have a higher priority than the standard telegrams with support from the Ethernet prioritisation mechanisms.

An optimised real-time protocol stack is installed on the terminals, which considerably shortens telegram throughput times in comparison with the TCP/IP stack.

In this way, performance values comparable with Profibus can be achieved.

Most importantly, real-time Profinet is fully compatible with the IEEE802.3 Ethernet standard.

Of course building real-time capability into Profinet would mean nothing if the Ethernet hardware was not up the job for demanding motion applications.

Effective Ethernet switch technology, for example, is essential for machinery applications if OEMs are to achieve the desired flexibility of topology.

But conventional industrial switches certainly do not offer a real-time behaviour for isochronous drive control.

Recognising a need for support hardware, Siemens has developed the ERTEC enhanced real-time Ethernet controller ASIC.

This upgrades industrial Ethernet with the Profinet hardware-based synchronisation procedure with isochronous real time (IRT).

The ERTEC 400 with its integrated four-port real-time switch and 32bit microprocessor is a high-performance Ethernet controller developed especially for industrial use.

It provides isochronous real-time communication based on the IEEE802.3 transmission method.

And it intelligently combines cut through and store and forward switching mechanisms.

In this way, consistent plant and machine solutions can be realised that are compatible with the standard.

Further, the switch technology enables flexible topologies to be realised for the best possible adaptation to the plant or machine.

Any topology can be readily implemented, and changing between different media such as from copper to fibre or wireless becomes a simple matter.

A line can be made into a ring with the switch technology in order to create media redundancy.

Here, changeover takes place in the isochronous communication channel without interruption.

Hot plugging is also possible with Profinet.

This means that discrete elements of a larger machine - such as the labeling station of a bottling plant or the feeder of an enveloping machine - can be disconnected, modified or replaced without interrupting the operation of other parts of the machine.

With these latest developments, Profinet is providing a networking backbone that is enabling OEMs to design and build machines with ever-higher performance and ever more sophisticated capabilities.

Profinet is making it simple to employ greater numbers of drives and motion controllers, yet guaranteeing ever faster reaction times.

And there are still always sufficient reserves of capacity for concurrent, open IT communication, enabling users to realise the goals of forward-looking diagnosis and maintenance functions, and thus to optimise availability and improve logistics.

The bottom line is that Profinet is enabling high-performance machines to be realised more cost-effectively and more quickly by the OEM, with the dual benefit that the end user also profits across the board, in terms of flexibility, time to market and, ultimately, increased competitiveness.

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