OPC UA Server
PLCnext Technology controllers include an embedded OPC UA server and OPC UA client which are integrated alongside the controller runtime.
The OPC UA communication models are represented by the 'OPC UA' icon in the PLANT. Via this tree node, the models can be configured in PLCnext Engineer. The OPC UA configuration data are part of the PLCnext Engineer automation project and written to the controller with the project. The OPC UA server loads the project during the controller start and automatically executes it.
Purpose of the OPC UA server
The OPC UA server has the following purposes:- Read data item values on request of an OPC UA client from the running application process (which is automatically the only connected data source).
- Sample the data and provide it to the requesting OPC UA client(s).
- Optionally allow OPC UA clients access to selected paths of the file system of the PLCnext Technology controller.
Clients can receive data from the OPC UA server not only on explicit request. They can also subscribe variables (process data items), define a sampling interval for them, and then automatically receive updated values if, for example, a threshold value was exceeded or if the value of a subscribed variable has been modified or any other defined trigger has occurred.
Server-client communication
The communication between the server and its clients complies to the OPC Unified Architecture protocol. OPC Unified Architecture (UA) is a standardized protocol for the industrial machine-to-machine communication. It was defined by the OPC Foundation. Compared to previous OPC versions, OPC UA provides a new information model with improved semantic structuring of machine data, such as process data item values or parameters. OPC UA considerably facilitates the communication between server and clients.
In addition to the OPC UA Standard, a PLCopen standard defines an information model which has been adapted to the special requirements of automation applications. It specifies the information model an OPC UA server has to provide for the data of IEC 61131-compliant controllers to the environment. Visit the PLCopen website for further details.
Configuring the OPC UA server in PLCnext Engineer
The configuration of the OPC UA server is done using the 'Server Settings' editor (editor of the 'OPC UA' editor group). The editor provides the following categories: