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Oct
09

Basics of Fieldbus

When the Fieldbus Foundation was established, I lead the team that wrote the Function Block Application Process Specifications. This was a unique experience since it offered a rare opportunity to work with and to get to know some of the best control engineers from Siemens, Yokogawa, Honeywell, Leeds and Northrup, Foxboro, ABB, Smar and others leading companies in our industry.

In the committee meetings, we were able to put aside the commercial barriers that often prevent open discussions. In many cases, we used the ground breaking work by the SP50 User layer committee as a starting point in the development of the function block specifications. However, significant changes were made to incorporate the best ideas and features from existing products. Also, the architecture and formal model defined by Part 1 of the specification were written and structured to support object oriented design and implementation of field devices – something important if you are a manufacturer of field devices.

Basic architectural components such as status and mode definitions were discussed by the function block team at length and in the end reflected the contribution of more than one company. For example, the definition of status was strongly influence by Tom Kinney, Foxboro, and Bill Hodson, Leeds and Northrup. Similarly, the basic function block set defined in Part 2 of the specification were reviewed in detail to insure the blocks addressed the requirements of each company. The advanced function block set defined in Part 3 of the specification and the specialized blocks in Part 4 and 5 were defined by members of the team that had direct experience with the functionality encapsulated by the block.

When work on parts 1-3 of the Foundation Specification for the Function Block Application Process was completed in 1994, there were very few fieldbus products on the market and even fewer control systems that supported these devices. In the function block team we discussed the need to communicate the advantages of fieldbus to inform the industry of this technology. Thus, Tom Kinney, Foxboro, and Marcos Peluso, Smar, and I worked together to put on a fieldbus tutorial at ISA1995 conference. In this tutorial, we gave an overview of the technology to a standing room only audience. To show how fieldbus would be applied, we took a waste water process example and analyzed the benefits that fieldbus had over a traditional installation. For the next seven year, Marcos – who is now with Emerson – and I continued to host fieldbus a tutorial each year at ISA. In each tutorial, we focused on a different aspect of fieldbus installation and application. Much of the material that we developed for these tutorials can be found at Fieldbus Tutorial. If you are unfamiliar with fieldbus and want to quickly get up to speed on the basics then you may find the information provided at this site to be helpful.