Products Extending the
OPC Product Range
OPC stands for “OLE for Process Control” and describes an initiative for
standardization of data exchange in automation technology. Formerly, applications such as
operating and monitoring software were forced to use the differing access procedures of
each controller manufacturer. OPC is the specification for a uniform software interface,
independent of individual manufacturers, permitting access to process data from any
manufacturer in a consistent manner.
General features of the Beckhoff OPC Server
In addition to the OPC access to TwinCAT, Beckhoff is now offering an OPC Server solution
for its Control Panel products. Both the OPC Servers are being fundamentally restructured:
The result is that certified OPC products are available for DataAccess (DA) and
Alarm&Event (A&E).
DataAccess servers inform their clients at specified intervals of current process values. Alarm&Event Server provides various categories of events to their clients: Thus a “condition-related” event details information that an item of process data has passed above or below a previously specified limit.
DataAccess clients can obtain information about existing data items by reading the server‘s “namespace”. Alarm&Event servers make a corresponding “eventspace” available. Other functions can control the behavior of an A&E server: Events can be activated, deactivated or simply acknowledged.
The new Beckhoff OPC concept also includes open access to the configuration of the OPC Server via XML: As an alternative (or as an addition) to the Beckhoff OPC configuraton tool it is possible to configure the server via XML from existing customer database.
In addition to the namespace and the eventspace, other features of the Beckhoff OPC Server can be defined with the configuration tool, or via XML: Simulation signals allow the OPC client/server communication to be tested without accessing physical I/O. The simulation algorithm allows sinusoidal, ramp and random signals, e. g. to configure in amplitude, slope and offset and so on.
Also interesting is the new facility for the online conversion of process values: Configurable linear conversions allow process values in units of “degrees Celsius” to appear in the OPC client as “degrees Fahrenheit”, or “inches” as “centimeters”.
The DataAccess servers now also allow an OPC item to be defined as an array or structure: Example: An OPC client has to pass 5000 formula parameters via the TwinCAT OPC Server to TwinCAT PLC. Instead of
5000 distinct item calls now only one call is issued thus minimizing the operating system load. Data consistency into the destination device is of course ensured here.
TwinCAT OPC-Server
The OPC Server is an element of the proven TwinCAT system architecture: Individual parts
of the software (such as TwinCAT PLC, TwinCAT NC, …) are looked on as independent
devices, and the exchange of messages is handled through a consistent ADS interface. Since
the TwinCAT OPC Server uses this ADS communication, a wide variety of applications are
becoming available: Through the TwinCAT OPC Server it is possible to access all the ADS
devices such as TwinCAT PLC/NC/CAM/IO/CP. Through ADS, the Beckhoff Bus Terminal
Controllers and Beckhoff Fieldbus PLC Box products can be reached.
It is further possible to link any of the fieldbusses supported by TwinCAT: Lightbus, Profibus, Interbus, CANopen, DeviceNet, ControlNet, SERCOS interface, Ethernet, USB and generic DPRAM.
Control Panel OPC-Server
The Control Panel OPC Server permits easy access to the extended functionality of the
Control Panel. The status of the special keys, the LEDs or potentiometers is available
over the OPC standard interface. Also it is possible to lock out the keyboard, mouse or
Touch Pad, or to check the signals for the UPS (uninterruptible power supply).
Preconfigured XML files with descriptions of the Control Panel are linked to the OPC
Server, and are available as “namespace”. This allows the OPC client to find the
desired Control Panel functionality quickly.
The Control Panel OPC Server has been implemented for Windows 9x, Windows ME, Windows NT and Windows 2000 platforms.