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Local communication
Fieldbuses
Today, each part of a modern automation system must have the capacity to com-
municate and have uniform communication paths. Data communication require-
ments are increasing all the time, both horizontally on a field level and vertically
through more hierarchical levels. A fully integrated data communication solu-
tion for industry usually involves all these elements. This applies to everything:
sensor signals, which in turn are connected to instruments, valves, motors etc.
These underlying system components communicate with main control systems
or industrial computers where an application is executed.
This is the basis for the concept of fieldbuses, but what is a fieldbus really?
In simple terms you can say fieldbuses are a little like the Internet, but for industry.
Fundamentally they allow machines and other equipment to be linked to each other in
a network. This allows devices to communicate with each other and with other sys-
tems. When the idea emerged at the end of the eighties the driving force behind it
was the desire to shorten installation times and cable routing, in other words it should
be less expensive. Gradually this aspect has diminished in significance and today it is
more a question of the exchange of information. You can say that the fieldbus of
tomorrow will be more and more like the Internet and perhaps even based on the
same technology.
The international standardisation of fieldbus systems is vital as to how they are accept-
ed and established. IEC 61158 is a standard that describes fieldbuses, the standard has
the title: “Digital Data communication for measurement and control. Fieldbus for use
in industrial control systems’’ and is divided into 6 parts.
IEC 61158 Contents OSI layers
document
61158-1 Introduction
61158-2 Specification and definition of services Layer 1 Physical
61158-3 Service definition Layer 2 Data link
61158-4 Protocol specification Layer 2 Data link
61158-5 Service definition Layer 7 Application
61158-6 Protocol specification Layer 7 Application
B A C K