Geneva, Switzerland— When is an international fieldbus standard not standard? When it consists of eight non-interoperable protocols, according to some involved in the process.

Despite this proprietary pile-up, the eight-part IEC 61158 proposed fieldbus standard was approved in a 25-4 vote before Dec. 31, 1999, by participating national committee members of the International Electrotechnical Commission's (IEC) SC65C subcommittee. The vote gave IEC 61158 an 88% approval rate, far more than the 67% required for passage.

Four more positive votes from nonparticipating SC65C members pushed IEC 61158's overall approval to 88%, again more than the 75% required. Negative ballots were cast by Canada, France, the Russian Federation, and Japan. Italy abstained, while Brazil was not allowed to vote for nonpayment of dues.

Still in final draft international standard (FDIS) form, IEC 61158's Data Link Layer and Application Layer documents and results of the vote went back to the IEC's Committee of Action (CoA). The eight-part IEC 61158 was expected to secure the 10 positive CoA votes required for a two-thirds majority, making it the long-sought international fieldbus standard. If it falls short of final approval, then the CoA would discuss IEC 61158 further at its meeting in February or March.

"If this eight-part version is approved, we will have what's is called a catalog standard or a Chinese menu standard," says Dick Caro, convenor of SC65C's Working Group 6 (WG6). "Instead of giving users and vendors guidance, this will allow some vendors to claim their products meet an international standard. I think this would be very hollow and cheapens the idea of international standards."

Seven protocols were added to the proposed IEC 61158 fieldbus standard in October 1999. This followed a CoA ruling in June 1999, which required that a second protocol be added to IEC 61158. As a result, WG6 members met later that month in Ottawa, Canada, where they met with vendor representatives, who unveiled a "memorandum of understanding" signed two weeks earlier. After spending years fighting IEC 61158, the vendors joined at the last minute because it was on-track to become the international standard, even if a second protocol wasn't added.

This last-ditch effort resulted in the eight-part IEC 61158 now on the brink of final approval. It includes the original IEC 61158 protocols, plus tacked-on, parallel protocols from ControlNet, Profibus, Interbus, P-Net, WorldFIP, SwiftNet, and the Fieldbus Foundation's high-speed Ethernet protocol.

"Users have told me they're dissatisfied and feel disenfranchised by this whole process. They campaigned for a single standard, and now—bloop!—it's gone," adds Mr. Caro. "The vendors are just serving themselves. As a result, it's going to be much harder for a user to ask vendors to comply with part of a multiple standard, rather than comply with all of a single standard."