Is Ethernet ready for industry?

The relentless pace of recent developments in the global information and communication market has driven automation equipment suppliers towards new technologies. End-users can now derive unprecedented, tangible benefits in terms of cost, connectivity and flexibility. Web Application Hosting in PLCs, SCADA and intelligent field devices is now commonplace. Wireless networking is here today and is already proving useful, in applications like roving diagnostics. Here operators can make use of CE based mobile industrial communicators for Web browsing plant specific information. PC based control and monitoring systems are becoming more prevalent and industrial switching technology has improved significantly. Users now able to achieve fast media redundancy with open standard products.

The current dominance of Ethernet LAN technology is arguably at the centre of these trends when you consider its close association with the TCP/IP suite of protocols and the internet. Much recent debate, however, has centred on the further exploitation of Ethernet and TCP/IP in industrial applications, and in particular their use at the device level. At face value, this would appear to solve many specification and integration issues in addition to granting users access to relatively cheap IT components. However, there are a number of issues end-users need to consider in making investment decisions.

For industrial applications, Ethernet costs are not necessarily cheap when you consider the need for industrial twisted pair or fibre optic cables rather than office-type Cat 5 cables, which cannot provide the same level of noise immunity. More cable is generally required too as star topologies, rather than bus, have to be implemented. In addition, there is the need to add a switch rather than simple hub from the IT LAN in order to exploit the benefit of information access without the risk of bandwidth problems.

Ethernet is already quick enough to address the needs of many applications, particularly monitoring. However, there are arguably issues around determinism that have driven many controls vendors to develop middleware extensions to the User Datagram Protocol. This allows the use of Ethernet for time critical or control data. In choosing a bus, the general rule should still be that the worst case performance from the bus is 'good enough' for the application. For many printing, synchronising and machine tool applications using fieldbuses with millisecond responses, Ethernet is not yet an option.

The big issue to watch, however, is the application layer protocol. Ethernet and TCP/IP alone are not enough for devices to communicate over a bus. There needs to be a common application protocol between devices, whether it is Modbus, EtherNet IP, Fieldbus Foundation or another mechanism. Siemens' position on this has been to actively work with the Profibus User Organisation to assist in the development of the ProfiNet profile. Rather than tunnel an existing protocol onto the Ethernet, ProfiNet uses an industry standard mechanism - Microsoft's DCOM (Distributed Component Object Model) - to allow access from disparate devices over Ethernet TCP/IP. The approach looks set to better exploit the increasing benefit of IT technology in automation whilst recognising the strengths of today's fieldbus technology. The ProfiNet core specification team is ABB, Bosch, Moeller Electric and Siemens. It has completed a Version 1 specification, putting it ahead of most on the issue of better connectivity between the device and information levels in an organisation.

For the future, Ethernet will certainly be used more and more in automation. Developments in Ethernet technology look set to deliver astounding response times and bandwidth. However, the wire itself is arguably not as important an issue to industrial end-users in the new millennium as the connectivity of their systems. They must take into account the use and management of information available from the disparate systems that will offer Ethernet TCP/IP interfaces. The trick unfortunately, as with any fundamental shift in technology, is making sure you don't pick a technology now that has hidden costs or will restrict your options in the future when the market shakes out.

• Siemens Automation & Drives
  Email c100@industrialnetworking.co.uk