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In-Depth Information
first. Following this definition, industrial Ethernet changes into a fieldbus, even though many people
are inclined to associate it with LANs. However, this is just another evidence that the boundaries
between LANs and FANs are fading.
20.3 History
The question of what constitutes a fieldbus is closely linked to the evolution of these industrial
networks. The best approach to understanding the essence of the concepts is to review the history
and the intentions of the developers. his review will also falsify one of the common errors frequently
purported by marketing divisions of automation vendors: that fieldbus systems were a revolutionary
invention. They may have revolutionized automation, there is hardly any doubt about it. However,
they themselves were only a straightforward evolution that built on preexisting ideas and concepts.
20.3.1 Roots of Industrial Networks
Although the term “fieldbus” appeared only about years ago, the basic idea of field-level net-
works is much older. Still, the roots of modern fieldbus technology are mixed. Both classical electrical
engineering and computer science have contributed their share to the evolution, and we can identify
three major sources of influence:
•
Communication engineering with large-scale telephone networks
•
Instrumentation and measurement systems with parallel busses and real-time requirements
•
Computer science with the introduction of high-level protocol design
This early stage is depicted in Figure .. One foundation of automation data transfer has to be
seen in the classic telex networks, and also in standards for data transmission over telephone lines.
Large distances called for serial data transmission, and many of these comparatively early standards
still exist, like V. (data transmission over telephone lines) and X. (data transmission over special
data lines). Various protocols have been defined, mostly described in state machine diagrams and
Centronics
CAMAC
GPIB
RS 485
Parallel
printer
interfaces
Industrial
parallel
interfaces
Serial
interfaces
Telex
DT
Teletex
DT
Fieldbus
systems
SS7
V.21
X.21
DT in telecom-
munications
Computer
WAN
X.25
FIGURE .
Historical roots of fieldbus systems. (From Sauter, T., in
The Industrial Communication Handbook
,
CRC Press, Boca Raton, FL, , .-.. With permission.)
