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Profinet - linking different worlds
An innovative
concept, just taking off - Profinet opens up Profibus technology
to the production and corporate management levels in a company
In recent times,
there has been integration of industrial automation with the IT
of the higher levels of the office world in a company. Profinet
presents an open and consistent concept for the vertical integration
of Profibus. The use of Ethernet ensures both the openness and the
consistency of the concept
The profinet
concept represents the basis for an open, manufacturer-independent,
distributed automation and engineering system, whereby Profinet
only defines the minimum common features necessary. For this purpose,
Profinet relies on the existing product range and expands or supplements
the functions required for distributed automation.
The openness
and consistency of the Profinet approach is based on the use of
established and widespread market standards:
- Automation
object model to Microsoft COM/DCOM standard
- Communication:
TCP(UDP)/IP and DCOM wire protocol
- Object handling
in the engineering and HMI: Microsoft OLE, ActiveX.
The principle
can be described using a simple but very effective equation:
Profinet
= Profibus + open consistent communication with Profibus and the
IT standard Ethernet + manufacturer-independent engineering model
+ distributed automation through an open object model
In 1999, Profibus
International began searching for solutions to open Profibus technology
up to the production and corporate management level in a company.
One of
the main objectives was to find a structure for the vertical expansion
that, on the one hand, allowed existing openness to remain completely
intact and, on the other hand, one that permitted the seamless integration
of system sections on the basis of the widely available conventional
Profibus. With Profinet, the aspect of openness has been even further
expanded as Profinet offers an open interface to the entire world
of field buses.
This allows easy integration of all fieldbus solutions into a Profinet
system.
A further objective
was to ensure a far-reaching consistency that enabled users at all
levels to communicate and cooperate using equivalent mechanisms.
This aspect includes both horizontal communication between automation
devices (automation integration) and vertical communication between
users of office, management and field level (business integration).
The object-orientated component model provides the basis for this
concept.
With Profinet,
particular attention was paid to uniform, plant-wide engineering
based on a uniform data model. It was considered essential to enable
the creation of applications through the graphical, textual or script-based
interconnection of objects, thus enabling intuitive and easy handling
of tools.
The Profinet
concept covers all operational phases of a distributed automation
system and comprises the following key aspects:
- Open object
model for highly distributed automation systems (architecture
model)
- Open object-orientated
run-time-communication concept on the basis of Ethernet (communication
relationships between functional units)
- Manufacturer-independent
engineering concept (application development).
On the basis
of this overall concept, Profibus International has produced an
automation solution that not only allows connection of all bus suppliers,
but also
enables direct communication with IT of higher company levels.
According to
the current level of knowledge, an open object model offers a sound
basis for a uniform architectural concept for highly distributed
automation systems, from I/O level through to management level.
This basis allows the seamless integration of systems using conventional
Profibus technology into the overall system. Furthermore, an open
object model enables simple integration of any fieldbus system into
a Profinet system via proxies.
The architectural
concept of Profinet is based on COM objects (Component Object Model)
as defined by Microsoft. This allows the development of applications
on the basis of ready-made components.
The components
are set up in the form of objects that communicate with one another
through defined interfaces. A COM interface combines a specific
number of functions that can be described in the Interface Definition
Language (IDL). As far as the user is concerned, a COM component
is simply a number of interfaces. By calling a function of an interface,
the client accesses the services of such a component.
Because the
necessary interfaces are standardised, the tools for assembling
applications from ready-made components can be acquired from any
system supplier. INOC
- Profibus
International
Email b105@industrialnetworking.co.uk
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Profinet
distinguishes between objects in the engineering system (ES
object) and objects in the runtime system (RT object). The
Profinet concept follows the basic idea that each RT object
in the runtime system corresponds exactly to an ES object
in the engineering system. In this manner, relationships between
ES objects can be easily mapped onto the relationships between
the corresponding RT objects. These statements apply to both
the engineering representatives of the devices (ES device)
and the software (ES auto).
In this
concept, the ES objects and RT objects are regarded as two
different objects because, firstly, configuration is to take
place at a time at which the runtime world (devices) is not
yet available, and secondly, the function of the objects varies,
as only the RT object can produce the actual automation functionality.
The runtime communication runs via the interfaces of the COM
objects in the form of an object protocol based on the sketched
object model.
The runtime
model represents the actual objects available on a device
that are externally accessible through OLE automation with
their interfaces and methods and the relation of the individual
objects to one another. It does not make any assumptions concerning
the implementation of the interfaces, thus maintaining maximum
flexibility during an implementation as long as the impression
of the object is maintained on the communication line of the
device.
The runtime
concept is based on conventional Ethernet mechanisms for communication,
such as TCP/IP or UDP. This basic mechanism was then enhanced
with RPC and DCOM mechanisms. DCOM can be seen as an expansion
of COM technology for distributed applications based on RPC.
Alternatively, an optimised real-time communication mechanism
is made available for application areas with critical real
time.
The Profinet
components are mapped during runtime in the form of DCOM objects
whose communication is ensured through the mechanisms of the
object protocol. Automation objects (ie COM objects) appear
on the communication line as PDU in a form defined by the
DCOM protocol. Through the DCOM wire protocol, the DCOM defines
both the identification of an object and the method with the
associated interface and parameters. This enables transmission
of standardised DCOM packets on the communication line that
are determined through the interface definition. These packets
are generated in the client and evaluated and interpreted
in the server. A particular feature of this is that no COM
objects need to be available within the server. It suffices
that the implementation generates a so-called 'illusion of
an object' at the bus.
The setting
up of communication relations and the exchange of data between
the devices for the configured interconnection is ensured
by the ACCO (Active Control Connection Object). The transmission
itself is event-controlled. The ACCO is also responsible for
error recovery. This includes transmission of the quality
code and time stamp, the monitoring of the connection partners,
the re-establishment of a connection after connection loss
and test/diagnostics for interconnections.
With
Profinet, the automation objects (RT autos) running on Profinet
devices communicate with one another during runtime. The boundary
conditions and connections of the communication are defined
during the engineering process. For this purpose, an engineering
object model was defined which determines the technical framework
conditions for using ES autos (engineering automation objects).
This uniform model basis enables the combination of ES autos
of various manufacturers as well as the development of engineering
tools by various manufacturers.
This
engineering object model enables not only the development
of configuration tools that can use the components of different
manufacturers, but it also allows the specification of manufacturer
or application-orientated function expansions by means of
so-called facets. The clear separation between the manufacturer-dependent
programming of the devices themselves (component generation)
and the installation-wide interconnection with a higher-level
engineering tool (application configuration) allows products
of different manufacturers to be integrated in a single plant.
The ES
Autos are delivered by the component manufacturers or are
programmed by the application developers and then integrated
in the library of the configuration tool. The manufacturers
use appropriate firmware programming tools to program devices
with fixed functionalities, while the device suppliers offer
tools for programming loadable autos. An application is created
from components via the configuration tool.
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- Profibus
International
Email b105@industrialnetworking.co.uk
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