Profibus

Profibus is an international vendor-independent, open fieldbus standard based on the European fieldbus standard EN 50 170. Although applicable to CNC machine I/O, it was created for a much broader segment of industry that includes building automation, industrial automation and process control. Profibus serves as the communications system for exchanging information between automation systems and distributed intelligent field devices such as actuators, valves, flow control devices, variable speed drives, and so on. Both high-speed time critical data transmissions and complex communication tasks can be accomplished using Profibus.

It is interesting to note that both Profibus and the CAN architecture that DeviceNet is built on originated in Germany. CAN is from Robert Bosch GmbH and Profibus is from Siemens. Also, both groups have created separate organizations to develop and administer their respective technologies with the purpose in mind of guaranteeing openness and interoperability. For DeviceNet, it is the Open DeviceNet Vendors Association (ODVA) and for Profibus it is the Profibus Trade Organization (PTO).

The Profibus Trade Organization, supported by Siemens and many European vendors who guarantee device interopera-bility, publishes a list of benefits. The benefits of Profibus as presented by the PTO are very similar to those presented by DeviceNet's ODVA. The list includes the following.

• Open vendor independent protocol
• Plug & play capability
• Products validated through the PTO's certification process
• Reduced operational cost
• Faster installation
• Easier commissioning
• Greater flexibility
• Easier maintenance
• Faster access to production and diagnostic data
• Higher productivity with less downtime

Advocates of Profibus and DeviceNet each proclaim their networks to be the global market leader for connecting open intelligent devices. So how can both be right? It turns out that each is addressing a slightly different market segment. Profibus addresses the more complex and costly segment of the market, focusing significant effort on applications in the food processing, brewing, pharmaceuticals, chemicals, petroleum and petrochemical industries. To accomplish the task of meeting the needs in these industries, as well as those of manufacturing, two compatible buses have been developed under the Profibus technology: A high-speed Profibus-DP (Decentralized Peripheral or H2) for factory automation, and the Profibus_PA (Process Automation or H1).

Profibus' strongest position is in Europe with Germany, Italy and France leading in applications. The Profibus User Group estimated that, as of June 1998, there were more than 2 million Profibus nodes in use worldwide in over 200,000 applications. This installed base is estimated to be worth in excess of $4.5 billion. Currently there are over 1,700 catalog products, provided by 260 vendors, available.

Both Profibus and DeviceNet recognize the importance of extending office and engineering local area network com-munications to the device level, and both are working on plans to incorporate Ethernet into each of their networks. Profibus International is working on a new specification to be completed before the end of 1999 that will allow application functions to be mapped to Ethernet, TCP/IP. When implemented this will allow Profibus users to combine the features of Ethernet at the control level with the strengths of Profibus communications at the device level. Adding Ethernet capability will enable programming and diagnostic functions between Profibus networks via Ethernet as well as allow access to the Internet, a capability with growing importance as we move into the 21st century.

Last month's column closed with a comment that the trend is clear that CNCs will be required to connect to intelligent devices and that users and machine tool builders will probably not agree on a single intelligent device protocol. The control builders who are able to offer both Profibus and DeviceNet will enjoy the broadest market. Profibus is less likely to be used in CNC applications today because it addresses the higher complexity and higher cost devices, but the trend in intelligent devices is to become more complex and smarter, which is a plus for the future of Profibus.