wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

5-2 Industrial Communication Systems
Engineering
tool A
Portability
Configurability
Engineering
tool B
Industrial
communication system
Interoperability
FB
(function i)
Functionblock
(FB)
Functionblock
(FB)
FB
(function i)
Automation device x
Automation device y
FIGURE 5.1
Distributed automation system.
to consider not only the physical connection but also different other levels. This ability to cooperate can
be described by different terms.
Two components need to have identical properties to reach a certain level of cooperation. These five
properties are
1. Identical communication protocol on layer 1–7
2. Usage of services by the application
3. Definition of the interface variables regarding, for example, data type, resolution, or measuring unit
4. Semantics of the application (algorithms, amount, and meaning of interface variables)
5. Dynamic behavior regarding, for example, control parameters or filter constants
Depending on the number of properties that a system fulfills, we can assign the following terms (Table 5.1):
Compatible and interconnectable require loosely defined communication agreements; the components
must not interfere with each other, which translate to requirements on the physical channel, for
example, voltage level or bitrates. Interworkable systems need to have an agreement on the meaning of
transmitted information in terms of data types (e.g., how many bytes make up a number?, is it an integer
or a floating point?) and also have to define error values in case a value cannot be transmitted (e.g.,
too big or sensor is broken). An example for this level of cooperation can be found in local operating
network (LON) [1], where standard network variable types (SNVTs) have been defined. For example, the
type snvt_temp defines temperature, which can be used for transmitting common temperatures with
the following properties:
• Data type: unsigned long integer
• Total length: two bytes
• Measuring unit and range: degree Celsius ranging from −274°C to +6279.5°C
• Resolution: 0.1°C
On this level, the user of the system can be sure that the components do not interfere with each
other, that they can exchange data, and also have the same understanding of the interpretation of
TABLE 5.1 Term Definitions by Properties
1–5 Given above
Incompatible None
Compatible 1
Interconnectable 1 2
Interworkable 1 2 3
Interoperable 1 2 3 4
Interchangeable 1 2 3 4 5
© 2011 by Taylor and Francis Group, LLC