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Profibus PA
Profibus PA (Process Automation) was developed by the Profibus User Organization (PNO) as a lower-speed intrinsically safe counterpart to Profibus DP for applications in process environments. Like H1 Foundation Fieldbus, Profibus PA is a digital replacement for 4-20 mA analog signaling for process field devices such as pressure transmitters, flowmeters, and valve positioners. Siemens is a driving force behind the development of both Profibus DP and PA. When the former Interoperable Systems Project (ISP) split up in the early ‘90s, Siemens was left with the technology developed by the ISP and incorporated it into Profibus PA.
Profibus PA is essentially Profibus DP technology superimposed on the standard IEC 1158-2 standard fieldbus physical layer, which is the same physical layer standard used by the Fieldbus Foundation. Several extensions were added to Profibus DP to make it appropriate for process applications in the form of Profibus PA.
These extensions include acyclic read or write
of process data, confirmation of diagnostic and alarm messages, transmission
of device status, bus power and intrinsic safety. PA uses basic Profibus
DP functions for the transmission of measured values and status, and extended
Profibus DP functions for parameterization and operation of field devices.
(See Figure 9).
Geographic Differences Drive Fieldbus Competition
Geographic strengths and weaknesses will have a major impact on fieldbus acceptance and penetration. Currently, the two major camps of Fieldbus Foundation and Profibus PA both have different geographic strengths and weaknesses. With headquarters in Austin, Texas, the Fieldbus Foundation has the support of powerful field device and control system suppliers in North America and Japan. Fisher-Rosemount, for example, was the primary driving force behind the formation of the Fieldbus Foundation through the merger of the WorldFIP North America and ISP fieldbus development projects. Other key FF supporters include Honeywell, Foxboro and Yokogawa Electric. It is interesting to note that Fisher-Rosemount, Honeywell, Foxboro and Yokogawa have no plans to introduce Profibus PA-compatible field devices in the near future.
While Fieldbus Foundation has a strong base of North American suppliers, Profibus PA and the PNO have a decidedly European flavor. The driving force behind the formation of the PNO and the development of Profibus PA, for example, is German-based automation supplier Siemens. Siemens, Klockner-Moeller and Robert Bosch originally developed the Profibus protocol before handing it over to the independent PNO. Siemens was also a member of the now defunct ISP, and retained the rights to ISP technology after the group’s dissolution. Siemens has no immediate plans to introduce Fieldbus Foundation-compatible products.
While Siemens is strong in the European DCS market, the company entered the European field device market relatively recently through the introduction of its own line of pressure transmitters, smart positioners and flowmeter products. Outside of Europe, Siemens is a much smaller player in both the DCS and field device markets.
Some suppliers, such as Elsag Bailey and ABB,
will support both Foundation Fieldbus and Profibus PA in their products.
ARC, however, expects that these suppliers will primarily offer Profibus
PA products in Europe while FF products will be offered in North America.
Elsag Bailey, for example, will offer Profibus PA-compatible field devices
through its recently acquired Hartmann & Braun and Schoppe & Faeser
businesses in Germany and the rest of Europe. In North America, the company
will offer FF-compatible field devices. (See Figure 10).
Beta Site Locales Indicate Future Geographic Strengths
Beta test sites are further evidence of the geographic boundaries surrounding fieldbus. Fieldbus Foundation has conducted 2 beta sites in North America and one in Japan. Fisher-Rosemount just announced its first installation of FF-compatible control systems and instruments in Saskatchewan, Canada. Conversely, all Profibus PA beta sites to date have been European installations, with the majority of beta sites in Germany.
The Japanese beta test for Fieldbus Foundation reflects the strong commitment that most major Japanese process control suppliers have for FF. Major suppliers such as Yokogawa Electric, Fuji Electric, and Yamatake-Honeywell plan to offer FF-compatible field devices, while none of these suppliers currently support Profibus PA. In ARC’s opinion, this could be a serious drawback to penetration of PA not only in Japan, but also in other developing Asian markets where both Japanese and North American suppliers have a controlling interest. Siemens, however, does have a presence in the Asian DCS market, particularly in countries such as India and China. The PNO, for example, recently held a conference in China to promote Profibus DP and Profibus PA.
Strength in Asian markets will be an important
factor in the long-term success of both Foundation Fieldbus and Profibus
PA. While North America and Europe are leaders in the adoption of new technologies,
the markets for control systems and field devices in these countries are
mature. Developing regions such as Asia are experiencing explosive growth.
Most of this growth is coming from new plant construction, where fieldbus
has the greatest impact on cost savings. The race to establish a successful
installed base of fieldbus systems in Asia may determine the outcome of
the overall battle for fieldbus dominance. (See Figure 11).
