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

Profiles and Interoperability 5-3
these data. However, this does not ensure that the components can also cooperate seamlessly. In addition
to an understanding of values, the components need to be designed toward other requirements.
For one, there is the direction from where communication is triggered: A node can either send its
information regularly to any component that is interested in the value or it can wait until another
component queries it for its value. A controller component on the other side has to implement error
behavior in case a required value cannot be retrieved, for example, due to communication failure or
failure of a sensor component. In some cases, it may be necessary to calibrate a sensor component.
A controller component has to consider the fact that during calibration, the component is unable
to deliver a reliable measurement. These issues are beyond mere communication; they relate to the
functionality of a component.
In an interoperable system, the devices from different suppliers have to be able to exchange information
and to use the information that has been exchanged [1]. If a system is capable of communicating
and exchanging data, it is syntactically interoperable. When a device is able to process such
data with useful results, it is semantically interoperable. To achieve interoperable or interchangeable
components, the functions of the components have to be standardized. This includes defining groups
of components, for example, sensor, actuator or controller and their properties, for example, their
time response. In LON, this level of cooperation is achieved by defining functional profiles. On this
level, it is possible to achieve true interoperability, which means that components (e.g., from different
manufacturers) can be combined to one system to cooperatively provide the system functionality.
Components can be replaced (also by components of other manufacturers) without affecting
functionality.
The function blocks shown in Figure 5.1 consist of programs, data, and communication services
(Figure 5.2). To ensure interoperability between distributed function blocks for one control function,
we have to standardize the functions, data, and communication services of the function blocks in a
functional profile.
Users benefit from standardized components by being able to use components, which can be manufactured
by different companies. Manufacturers on the other side can extend their market segment
by offering only parts or single components of a system and do not have to offer all components
of a system. Generally, standardized distributed systems that are interoperable have the following
advantages:
• Automation systems can be built up with autonomous subsystems.
• Autonomous subsystems can be manufactured and tested independently from the complete
system.
• Subsystems from different manufacturers can be integrated.
• Existing systems can be easily extended with new automation devices.
• Integration of automation devices can be done by configuration.
Industrial communication system
Function block n.1
Communication services
Functional profile
Function block n.2
Communication services
Program
Data
Specif.
func.
n.1
Specif.
func.
n.2
Program
Data
Automation device x
Automation device x
FIGURE 5.2
Distributed automation function.
© 2011 by Taylor and Francis Group, LLC