PLCnext embedded OPC UA server (eUA)


OPC Unified Architecture (UA) is a standardized protocol for industrial IT and OT communication. On request, an OPC UA server provides an OPC UA client with process data and variable values from a running application.The PLCnext controllers contain an embedded OPC UA server (eUA). In addition to the runtime, it is integrated in the controller. It enables access to components, programs, function blocks, structures and variables of PLCnext Technology.



You can exchange alarm and status messages between a program and the eUA server. For additional information, please refer to the Alarms section.


An OPC UA client can subscribe to a list of variables that are then monitored for changes by the GDS. The variables are checked for changes at a defined interval. If a changed variable is detected during the cyclic check, the GDS informs the OPC UA server, which forwards the message to the client. When subscribing to a variable, the client can define a sample rate, which is then served by the server. You can choose from predefined sample rates. Sample rates are device-specific.

The sample rates for the AXF F 2152 controller are defined as follows, for example:

  • 100 ms
  • 250 ms
  • 500 ms
  • 1000 ms
  • 2000 ms
  • 5000 ms

If an OPC UA client requests a variable with the desired rate of 600 ms, for example, it will be assigned to the 500 ms group. The server assigns the subscription to the group nearest to the desired value and returns this value to the client as RevisedSamplingInterval.

Data types

For a mapping table containing the PLCnext Technology data types and the corresponding OPC UA data type, see Available data types.


For information about the OPC UA namespaces See here.

UA server endpoints

The eUA server offers an endpoint to which the clients can connect. In its URL, you can either configure the IP address of the controller or the DNS name. Implement the configuration in the PLCnext Engineer software:

In PLCnext Engineer, open the OPC UA node in the PLANT area.

In the Basic settings, enter either the DNS name or the IP address in the input field.


Encryption algorithms

You can offer the following encryption algorithms for the endpoints to the OPC UA clients:

  • Basic 128 RSA15*
  • Basic 256
  • Basic 256 SHA256

*Note: By default, the Basic 128 RSA15 encryption algorithm is not activated as this algorithm is no longer regarded as secure. However, you can activate this algorithm to be able to connect the eUA server to older OPC UA clients that at most support this algorithm.

Ethernet ports at the controller

Currently, there is no mapping to a certain Ethernet port at the controller. Therefore, a connection is possible via all ports.

Disabling user authentication

You can also work without security settings. To this end, deactivate the user authentication via the web-based management of your controller.

Note: If the user authentication is disabled, the OPC UA client does not have to authenticate itself to the OPC UA server. This way, unrestricted access to the OPC UA server is possible.





 • Published/reviewed: 2020-03-29 •  Rev. 24