Ethernet meets fieldbus

In recent years, Ethernet and TCP/IP standards have established themselves in local networks in the office environment. The world of automation has been considering whether these basic technologies can also be transferred from a high-volume market into the area of automation technology. Is Ethernet the field bus of the future and can existing fieldbus standards be replaced by Ethernet? There is no single answer to this, but automation designs will change if Ethernet is used. Using Ethernet and the related internet technologies, the change from today's centrally organised automation designs to future decentralised designs with distributed intelligence becomes possible.

Communications systems in future automation applications must demonstrate certain key characteristics. Firstly there must be rapid and simple reading of the signals from peripheral devices; an open design, controllability and a system's deterministic characteristics play a decisive role here. Secondly, in hazardous environments it must be possible for safety information to be transmitted through a protocol tested and certified by the TÜV and BG. Thirdly it must be possible to synchronise drives accurately and speedily, since drives and drive systems will play an increasingly important part in future designs. Drives will take over more and more responsibilities from present-day control systems and will autonomously control individual functional units within a complete installation. Lastly it must be possible to establish end-to-end communication between office and production.

Future automation applications are going to be characterised by uniform platforms and modular application software. More and more use will be made of uniform system platforms, which will be strongly influenced by developments in the commercial world. TCP/IP will be used as the end-to-end communication protocol and the uniform hardware standard will be based around a PC, running Windows and using an internet browser as the universal operator interface. Machines and installations will be constructed from modular functional units which will be supplied pre-assembled off the shelf and plugged together to make a machine. There will be decentralisation of intelligence and functionality which means that a central control system will be replaced by any number of dispersed intelligent systems. Machine design will become easier and more flexible, and commissioning and maintenance costs will be reduced. The application of standards throughout will enable products from different manufacturers to be used.

Extensive examination of communication standards for possible use in future automation designs has shown that some are capable of meeting all technical requirements, but they tend to be too complex and too expensive. Other standards are stronger from an economic point of view but on their own are not capable of meeting all the requirements, and Ethernet is one of these. However, by combining Ethernet, a fieldbus such as Interbus and the readily available protocol TCP/IP, the demands of future communication systems in automation applications can be covered.

The main arguments against the use of Ethernet in applications close to industrial processes are its lack of determinism and its unsuitability for industrial environments. In order to make up for these shortcomings, Phoenix Contact has developed its FactoryLine product range. The TCP/IP protocol has been implemented on Interbus which makes it possible to address an intelligent device transparently. File transfer is possible using standard FTP, and with their complementary features Ethernet and Interbus form an end-to-end communications system. This does everything required within a machine and on the factory floor as well as linking together office and plant. Interbus is the installation system in the switch cabinet and in the field, and is used to implement rapid machinery control systems and for synchronisation of drives. TCP/IP is the underlying communication protocol in all these systems, making end-to-end communication with intelligent field devices possible by the use of standards such as FTP or HTTP.

• Phoenix Contact
  g101@industrialnetworking.co.uk