Lenze DriveServer Erste Schritte - Handbuch (Seite 40)

DriveServer
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38 DriveServer DE/EN 1.1
2.2 OLE for Process Control
OLE for Process Control (OPC) defines an interface based on Microsoft Windows technologies OLE, COM and
DCOM which enables data exchange between different automation units and PC programs without having any
problems with drivers and interfaces.
Sometimes, this tool is also called “Software plug”, because programs made by different manufacturers can be
easily connected for communication. More and more manufacturers of visualisation systems use OPC since it is
then possible to do without special drivers for different units.
OPC was created in 1996 in the United States and since then has been spread in the automation industry. The
user group OPC Foundation comprises more than 150 companies, among them is Lenze.
Main
structure
The main structure of OPC is a client-server system. An OPC server provides data which can be read from a drive
via a fieldbus system. These data can be accessed through an OPC client (e.g. parameter setting program,
visualisation). Depending on the data, changes via the OPC client are also possible. Several OPC clients can
access one or several OPC servers (n:n connection) at the same time.
Items/Groups Usually data is exchanged via so-called OPC items which are represented by process variables and unit
parameters (codes). OPC items can be arranged in OPC groups according to logical or dynamic aspects. Thus, for
instance, all OPC items which are to be updated following the same time cycle, can be saved in the same OPC
group. OPC items and OPC groups are always in the OPC server. OPC clients log on the OPC server and list the
OPC items to be accessed.
OPC items also have specific properties. A property is a feature which informs the user, for instance, about the
value limits or units of an OPC item.
Browse
function
In addition to the functions Read and Write of OPC items, most OPC clients also support the Browse function. The
Browse function helps the OPC client to find all OPC items (also parameters) available on an OPC server.
Since most OPC servers require the configuration of OPC items, it can sometimes be very costly to configure all
parameters of a drive. The DriveServer however automatically detects the all drives connected and displays all
parameters available in a logical order when using the Browse function. The user only has to select the
parameters to be accessed from the OPC client.
COM/DCOM Since OPC is based on the Microsoft Windows technologies COM and DCOM it is also possible to access an OPC
server from several computers via a local network. For instance, the OPC server can be on an industrial PC in the
field and the OPC client can be a PC in an office, the two can be connected via a LAN (Local Area Network), such
as Ethernet. The standardised OPC interface also enables the data transfer from the drive into the Internet.
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