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

25-8 Industrial Communication Systems
is compared with the corresponding data of the operation system to recognize inconsistencies of the
values. Likewise, the quantities and qualities of final products are observed by systems concerned with
the product distribution and delivery. Systems concerned with maintenance need information from the
operation system for recording the operation time of equipment. Other systems are employed for quality
assurance and control, and in order to mark product samples and quality measurements with time
stamps, these systems need to work closely with the operation system [BR05].
25.3 Currently Applied Communication Systems
Corresponding to the general concept of the automation pyramid, different means of communication
are applied according to the requirements at each level. More data need to be transported on the higher
level while the real-time capabilities are of less importance than on the lower levels. Hence, the communication
layers can be distinguished as follows:
• Ethernet is commonly used for the communication between the actual process control entities
and any support systems such as supervisory control and data acquisition (SCADA) systems.
With respect to the structure presented in Figure 25.3, Ethernet realizes most of the shown information
connections.
• For the communication between the process control entities such as PLCs, which will happen
most likely on the phase layer of the procedural control model, fieldbus technologies are
commonly applied. While PROFIBUS represents the market leader on the European market,
ControlNet is one competitor on the Anglican markets. However, also several other technologies
(e.g., CANopen, DeviceNet) are in use and the share of industrial Ethernet on the market is
currently increasing.
• The situation is similar to the communication between the process control entities and their allocated
peripheral I/O-modules. However, the real-time capabilities are of a vital importance at
this level of communication. This type of communication realizes only basic functionality of the
automation components without procedural activities and can therefore not be allocated to a layer
of the IEC 61512 models.
• With respect to the communication of I/O-modules with their assigned sensor/actuator units,
fieldbus technologies such as PROFIBUS-PA, DeviceNet, FOUNDATION fieldbus, or the
AS-Interface (AS-i) are commonly applied. Also the HART Protocol represents a common fieldbus
for this level of communication. However, even though the number of sensor/actuator units
with fieldbus technology is rising, the majority of currently employed sensor/actuator units is still
connected via ordinary wires to the I/O-modules. Also this type of communication cannot be
allocated to a layer of the IEC 61512 models.
A result of all these different networks is a high integration effort. This is especially a problem if
one system has to support different communication technologies. Therefore, attempts are undertaken
to unify the interaction of control systems and control equipment. An approach targeting the level of
control units and SCADA systems is the new OPC unified architecture (OPC UA) specification from the
OPC foundation (http://www.opcfoundation.org). This specification defines at a high level and network
independently how control equipment can exchange data. However, in its current implementation, it
relies on Ethernet technology and is therefore not suitable for all types of control equipment.
25.4 Upcoming Requirements of Distributed Process Automation
Industrial automation—including process automation—is currently faced with a major paradigm
change. Our globalized markets are getting more volatile. Customers are getting more discerning and
favors customized special products. This leads to shorter product life cycles, smaller lot sizes, and less
predictable sales volume. Especially, for the process automation domain, this new environment is very
© 2011 by Taylor and Francis Group, LLC