Device-specific OPC UA® settings and limitations

OPC UA server

The PLCnext Technology controllers have the following device-specific default OPC UA® settings:

Target Maximum number of sessions Minimum supported sample rate Available sample rates
AXC F 1152 3 100 100, 250, 500, 1000, 2000, 5000
AXC F 2152 5 100 100, 250, 500, 1000, 2000, 5000
AXC F 3152 8 100 100, 250, 500, 1000, 2000, 5000
RFC 4072S 10
from 2023.6: 30 		50 50, 100, 250, 500, 1000, 2000, 5000
RFC 4072R 10
from 2023.6: 30 		50 50, 100, 250, 500, 1000, 2000, 5000

Up to firmware version 2023.3, the maximum number of sessions listed above are the upper limit.
From firmware version 2023.6, the maximum number of sessions listed above are preconfigured default values that can be changed in PLCnext Engineer from version 2023.6 if required. Higher values are also possible. 

Note: A further upper limit for the number of concurrent sessions is defined in the WBM in the Security area on the User Authentication page. On the tab Session Configuration in the field Maximum concurrent sessions the maximum number can be entered. Just like any communication to the PLC, each OPC UA session requires a user session. The default value of maximum concurrent user sessions is 32. Make sure that the configuration of the maximum number of OPC UA sessions matches the number of maximum concurrent sessions. See also Security - User Authentication - Maximum concurrent sessions
Note: It is the responsibility of the user to ensure that a CPU usage of about 80 % is not exceeded, visible in the PLCnext Engineer cockpit (show where to see the CPU loadshow where to see the CPU load) or in the WBM cockpit (available from firmware version 2023.0 LTS).

OPC UA client

The OPC UA® client does not limit the number of connected servers, variable groups or variables within a group. This is to support different applications where the client is either a small extension using a few resources or where the client is the main part of the application.

Note: It is the responsibility of the user to ensure that a CPU usage of about 80 % is not exceeded, visible in the PLCnext Engineer cockpit (hide screenshotshow where to see the CPU load), or in the WBM cockpit (available from firmware version 2023.0 LTS).

see also OPC UA client

OPC UA PubSub

Starting with the 2022.0 LTS release, the PLCnext Technology firmware has an implementation of the OPC UA® Publish and Subscribe specification (PubSub) as a new communication mode. See also OPC UA PubSub.

The PubSub component and its quantity structure is limited.
The following values apply for the PLCnext Technology implementation:

  • Maximum network message size for all variable values of a ReaderGroup or WriterGroup: 1472 Bytes
  • Maximum number of connections: 4
  • Maximum number of WriterGroups: 8
  • Maximum number of ReaderGroups: 8
  • Maximum number of Writers: 32
  • Maximum number of Readers: 32
  • Maximum number of datasets: 32
  • Minimum publishing interval: 20 ms

• Published/reviewed: 2024-09-24   ☀  Revision 073 •