Fieldbus Chronicles: the Quest for a Unified Digital Standard

25 Years' of Perspective Chronicles Exciting Developments in Industrial Networking

By Paul Studebaker

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 Exciting developments in industrial networking were clearly among the driving forces behind then-Putman Publishing's decision to launch a magazine dedicated to process automation and control. Control's very first issue in October 1988 dove right into the topic, starting with a news story on the Manufacturing Automation Protocol/Technical Office Protocol (MAP/TOP) standard for communicating among "islands of information” in industrial environments.

A tutorial article detailed the anatomy of the International Organiiztion for Standardization's Open Systems Interconnect (ISO/OSI) model, and another article covered the ISA SP50 committee's progress toward a digital communications standard, which it had started working on in 1984.

That first issue also included a "Honeywell News” story, "The SP50 War,” where the company paid for space to explain its neutral position on the emerging standard: "In 1975, ISA's Standards Practices Committee, SP50, defined 4-20 mA as industry's analog fieldbus standard. Now, with digital sensors and actuators replacing analog components, SP50 has again convened, this time to define a new serial, digital, bi-directional communications protocol. During these interim years, several instrument and control manufacturers have forged ahead with their own digital communications architecture. The situation has raised some interesting questions.”

Honeywell counseled readers to understand the difficulty and importance of developing a truly interoperable
fieldbus standard. "Each manufacturer with its own protocol wants it adapted as the standard. None, however, meet the criteria.” Meanwhile, "Most likely, if you plan to invest in your system, there will be simple digital plug-ins available to convert your protocol to the new fieldbus…for example, Honeywell is developing a plug-in interface card that will link control room devices to the new standard and to the existing protocol in our smart transmitters.”

Development of a single standard was seen as imminent: "The SP50 committee should be submitting a draft for approval by 1990…you could be integrating SP50 components into your system sometime in 1991.” As the accompanying timeline shows, it took a lot longer to get a digital standard.

Some would say we never made it. Users wanted a standard that could do everything; vendors wanted a standard that would give their proprietary protocols a level playing field (if not a head start); and everybody wanted something they could hope to afford to implement. While SP50 and then IEC 61158 committees worked to establish a global standard, the Fieldbus Foundation, Profibus Trade Organization, Open DeviceNet Vendors Assn., HART Communication Foundation and others worked to develop and grow their own protocols and followings.

 See the timeline. 

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